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Updated : 08/08/2018 

"All is well, thank you very much for your help. 
Well worth the trip from Essex to North Wales.
J and J Heaton  13/7/2018".

STOP PRESS : Three cheers for Alpha Batteries, the first battery retailer we have seen that has a warning about AGM batteries needing the correct charger. Their website states -

"Please ensure your charging method can accommodate AGM batteries as charging at non AGM charge settings can adversely affect the life of the battery. Please contact us if you are unsure".

Well done those guys.


We do not sell batteries of any type, so this page is as independent as it gets.

Did you know that AGM batteries have performed so badly in automotive use that Audi, VW, Seat and Skoda have pulled them out of their cars and are moving back to Wet/Flooded Acid technology?

Allegedly BMW are preparing to do the same. Some BMW Dealers have been replacing failed AGM batteries with a Wet Acid technology version, Enhanced Flooded Batteries (EFB), for some years to very good effect. While 'Not so heavy duty on paper' EFB last much longer than AGM in real use. 

Landrover are also moving away from AGM. 

Mercedes have already swapped one of the two AGM batteries in the the highline cars to EFB technology, and the rumours are the other will follow soon.

Just like in Motorhome use, the general view in the battery industry is that AGM just don't deliver the promised performance.

If you look at the Banner web page (remember that Banner were the suppliers of the first AGM mass rollout in Motorhomes) you will see that almost all the new batteries are Flooded/Wet EFB technology. AGM hardly gets a look in. 

The website actually states that "EFB is the technology of the moment". See :

If you look at the RoadPro Frequently Asked Questions web page on batteries, one of the questions and answers is on AGM battery charging, it states -

"Q) What’s the best way to charge a Banner AGM battery?" 

RoadPro respond with -

"A) We recommend using an “intelligent” charger such as those from CTEK or Sterling. Some chargers may have a special AGM setting but, if they don’t, use the setting which gives a maximum voltage of 14.7V during the “bulk” and “absorption” stages and 13.6V during “float”. Don’t leave an AGM battery on charge indefinitely as it could be damaged".

RoadPro, the biggest Caravan and motorhome specific leisure battery retailer in the UK, are aware that the majority of battery chargers in Caravans and Motorhomes will not support an AGM battery. 

Indeed another Q/A on the same FAQ web page says that most of the chargers installed as standard won't even get an ordinary  wet acid battery "up to 80% – 85% of its maximum capacity". Hence the recommendation to fit specialist chargers that do have AGM optimised charging profiles.

The Roadpro web site FAQ page states - 

".... unless you are using an advanced charging system on your vehicle, you’ll probably end up with a battery that’s only half full. This is because most chargers built into vehicles will only charge the battery to 80% – 85% of its maximum capacity".

According to RoadPro "most" Caravan and Motorhome chargers that won't even charge a standard wet acid battery up to 85% will obviously be unsuited for a higher voltage AGM battery. 

We have seen some chargers struggling to get an AGM battery to 75%. 

Note how RoadPro's comment - "Don’t leave an AGM battery on charge indefinitely as it could be damaged" would also make an AGM unsuitable for a Solar install which is 'charging' day after day. 

We started this page some years ago because as far back as 2014 we began to see Motorhome and Caravan Electronics being damaged by prematurely degraded Absorbed Glass Mat (AGM) batteries. 

AGM batteries typically require a 14.8v charging rate for maximum performance and life when almost all the UK Motorhomes/Caravans have, at best, 14.4v, or at the worst, a 13.5v charger

We don't know of any Caravans that rolled off the production line up to 2017 with AGM optimised chargers. The new Sargent EC160 and Super 151 are fixed voltage (13.8v) low current chargers. Old fashioned 1980's style chargers yet these have been launched in the last year.

Only a very small percentage of Motorhomes actually have AGM optimised mains chargers capable of 14.8v charging. 

The problem of degraded AGM batteries has become so bad, some manufacturers are putting text on the casing showing a required charge voltage of 14.6v to 14.8v for optimum performance. 

LIke VMF in the photo below :

What other Lead Acid battery technology do you know that is so fussy about the correct voltage, the manufacturer prints it on the casing? 

For years Wet Acid batteries have happily tolerated recharge voltages from the 13.8v of a typical Caravan power supply/charger to the 16v output by Ford Cars and Vans. 

But AGM batteries are very fussy about several factors, not just voltages. 

AGM batteries can display deep cycle characteristics in laboratory tests, but only within very narrow confines and limitations of operation which are rarely achieved in the field. 

Confines such as an exact charging voltage, narrow band continuous current draw limitations, plus the most crucial : temperature operation. If the battery is operated outside these narrow limits, battery life won't be the 8 years life you have every right to expect from a £200 battery, but often less than two years. 

Did you know that when an AGM battery goes through it's Laboratory 'Cycle' testing to assess it's capability, it sits in a bath of Water to keep the temperature low and constant? With AGM batteries being so susceptible to temperature highs, it is likely to deliver more cycles in the Lab than real world Motorhome use.

Hymer fitted AGM batteries as standard habitation area units as early as 2013, without any regard for the none AGM charger that it was paired with. Their publicity said the AGM batteries would be fine on a 'Gel' profile setting. 
They weren't, they failed very quickly and often didn't charge up fully.

As a result Hymer spent a lot of money rushing through a mains charger that did have an AGM optimised voltage setting. 
But they didn't address the Alternator 'low charge' voltage, which wasn't optimised for AGM's need for 14.8v, so AGM batteries in Motorhomes continued to have short lives.

Only at the end of 2017/early 2018 did some Mercedes chassis have a device fitted to provide an uprated Alternator output.
However, we have now heard rumours that because AGM batteries have not performed even half as well as expected, plus the new revelations regarding AGM's withdrawal in the car industry, that the Motorhome manufacturers are considering their options. 

I received an email 3 years ago from someone who had read our pages on AGM batteries and wrote, 
"Allan, you are wrong about AGM. If they were not any good Hymer would not be fitting them as standard".

Can I just say to Mark, "If AGM's were any good, Audi/VW wouldn't be pulling them out now".

So why aren't AGM any good as a Motorhome Leisure battery? 

Well let's consult Victron Energy, the biggest specialist Deep Cycling battery and Battery Charger manufacturer in the World.

Aside from not being adequately charged by a Motorhome/Caravan charger, which we will cover later, AGM batteries have a very fine temperature operating window.

The below chart shows how half an AGM batteries life can be lost when operated at 'higher' temperatures. 
Just a 10 degree rise at the Plates, drops a high quality AGM batteries life down from 7 - 10 years to just 4 years.
A 20 degree rise at the Plates, not that different to the internal temperatures of a motorhome/caravan in Southern Spain in Summer, drops a 10 year AGM to a meagre 2 years life.

No wonder some consumers don't see an AGM battery last 12 months. 
These are not our charts and figures but the highly respected Victron Energy findings.
See the chart below :

30 degrees is not exactly a surface temperature that is going to burn your hands. The Leisure battery may be going through torture, yet the casing hardly feel warm. 
This is not an issue unique to Victron Energy batteries, which we rate as some of the best Batteries in the World, it is an issue with all VRLA batteries from all manufacturers and has been known for years. It is the reason why Datacentre UPS batteries are often in cool, air conditioned environments.

The Victron document also warns about the adverse impact to an AGM or Gel battery that prolonged charging/discharging at a higher than a 'normal' current will have in raising the Plate temperature. 

Just a small rise in continuous charge/discharge, raises the Plate temperature into the zone that can decimate AGM/Gel life, as noted above. 

See section 15 in the document :

"15. Charge current -
The charge current should preferably not exceed 0,2 C (20 A for a 100 Ah battery) otherwise the temperature of a battery will increase by more than 10°C"

If the battery is already warm at 30 degrees, then a 25amp charge/discharge rate will see it rise to 40 degrees, you can see the potentially catastrophic effect this will have on an AGM's battery life, 75% loss of life time, according to the chart above.

You can imagine what a 900watt/E Microwave drawing 140amps via an Inverter will do to an AGM? Yet some Battery Retailers actually recommend AGM batteries where high current draw will occur.

Note : The real electrical rating will be about 1,400watts as the 900w/E figure is only a guide to the 'Food Wattage', not that drawn from the 230v) 

Once you understand the above you begin to understand why the very latest cars still using AGM batteries have gone to such lengths to cool the batteries. 
One car we saw had the battery in the boot but took cooling air from the passenger compartment on the basis that the battery would only ever get a hard time when the car was occupied and the 'Air- con' activated to cool passengers.
It also had two temperature sensors on the AGM battery. If the ECU detected an elevated battery temperature it slowed down charging by the Energy Recovery System, or even shut it off altogether. 

That is maybe why the best battery charger manufacturers are now impressing the importance of temperature compensation charging with AGM's. 
Shame not one mainstream motorhome/caravan rolling off the production line up to Feb 2018 had it fitted as standard. 

Typically, conventional Wet Lead acid batteries suffer much less from temperature issues because the Acid is in a very fluid form, rising up the plates by convection and drawing fresh, cooler acid in from below. This keeps the Plate temperature significantly cooler. The mobile acid then carries the heat to the casing where it is dissipated. 

In an AGM the acid is almost immobile, absorbed in a Glass Matt, heat transferring only slowly away from the Plates. 

While conventional wet batteries can handle higher temperatures better than AGM/Gel, the Powerframe Varta LFD is more than twice as capable again. Extremely high temperature tolerant.

The chart below shows how, in hot desert conditions, a Varta/Bosch Powerframe battery outperformed a conventional wet acid battery by a ratio of better than 2 : 1.

So if 'conventional' Wet acid batteries outperform AGM, and Powerframe Bosch/Varta outperforms conventional 'wet's' by a massive 2 to 1 you can see the huge advantage a Varta Powerframe battery has over AGM with major resistance to loss of life from temperature and higher charging/discharging currents.
In real world Motorhome use, many batteries are used in the warmer months and/or warmer climes. The conditions that AGM batteries are likely to wilt under. In August 2018 Portugal was reporting temperatures over 40 degrees, it is likely the temperature inside the vehicle was nearer 50.

Factor in the poor charging regimes that almost all Motorhome/Caravan chargers and Alternators will deliver, and the much hyped cyclic capability will rarely ever be realised to even half that claimed.
Hence the many reports of short AGM battery life.

While the marketing leads us to believe that an AGM battery is tough, it is actually the most fragile of the Lead Acid technologies. Yes they can have a greater number of charge/discharge cycles than a conventional battery, but only if charging/discharging conditions, including temperature, are perfect. 

There is a very good reason why the Battery voted 2016 'Best for Trucks' is not an AGM, but a Wet/flooded battery.

The latest big Truck Battery from Yuasa, that was originally scheduled to be AGM, is rolling off the production line as an EFB. 

Below is the full Victron Energy Battery datasheet where the above chart, and all the other Victron charts we use, can be found, plus the text in full.

I went out to a Caravan charger repair and the couple said their BMW's AGM 'Stop/Start' battery had not lasted 3 years. Yet they lived in a rural area, not exactly roads with lots of high density traffic 'Stop Starts' to put a strain on the battery.

If an AGM battery that wants 14.8v is charged with 14.3v it will take longer to charge than a quality Wet acid battery.

On the 13.8v charger fitted in some Motorhomes it will take forever to charge up fully, and once it's been used for a few months, probably won't ever reach full charge due to internal degradation. 
If the charge from the Alternator at the habitation battery is also the more typical 14.1v at the battery (due to the normal voltage drop in many motorhomes caused by Fridge operation on 12v, dual batteries, etc) then that will further disadvantage an AGM in terms of both recharge time and percentage recharged. Potentially doubling recharge time and still only reaching 80% after many hours.

That might mean that when you come to use an AGM, it is only 85% charged, so may get discharged deeper than ideal, leading to even shorter life.   

Victron Energy Battery Datasheet.pdf Victron Energy Battery Datasheet.pdf
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The myth that AGM batteries don't lose fluid or Gas out fumes is also exagerated. They can and do gas, as shown by the document at the bottom of the page. 
An AGM battery has a valve in the top, the purpose of which is to maintain a higher pressure inside the battery to assist in recombining Hydrogen and Oxygen back to Water. Commonly known as Valve Regulated Lead Acid (VRLA) batteries. They are sometimes referred to as 'Sealed' batteries when they are not, as the Valve will, and does, open venting dangerous Hydrogen into the Motorhome.

Almost all Gel and AGM data sheets contain warnings not to install these batteries in an enclosed space because dangerous gas can build up. 


Some Charger manufacturers might tell you that their chargers are 'AGM compatible', but the AGM battery manufacturers websites disagree. Any old charger with more than about 13.5v may 'charge' an AGM battery, but it won't necessarily charge it properly or quickly. 

If a chargers advertising blurb states it is 'AGM compliant', but it does not have a separate 14.8v AGM specific charge profile, such as the Rovert charger range which has only 14.4v 'Wet' and 'Gel' settings, then the retailer doesn't know their product.

Schaudt, Victron Energy, Votronic, etc. spend thousands on developing charge profiles optimised to get the best from each battery Technology. I am pretty sure they would not spend that money if they could get away with a single profile? 

You can therefore imagine how good a Sargent EC500 will be, the manual states -

"the voltage rises to 14.4V to deliver the bulk charge to the battery.  When the battery is charged, the voltage is decreased at stage 3 to 13.6V to deliver a float charge to maintain the battery in the fully charged state".

Yet Sargent also say in the same EC 500 manual the above extract is taken from, "The PSU is configured to work with standard lead acid leisure batteries, and in most cases is also compatible with the latest range of Absorbed Glass Matt (AGM) batteries".

Clearly no modern Motorhome AGM Leisure battery is going to work that well or last with those voltages. But then the manual does have a 'get out' clause -   

"Before fitting non-standard batteries please check that the charging profile described in 3.3 is suitable for the type of battery by referring to the battery documentation or battery manufacturer".


Stop Start cars with AGM batteries are matched by Smart ECU controlled Alternators with voltages from a 13.5 'trickle' to up to 15.0 volts 'Boost' charge. 

If you accept what the top four battery manufacturers say, that their batteries should only be used with an AGM specific charger, and also accept that Car Stop/Start AGM equipped Alternators match this, then where is the  'AGM switch' on a Motorhome's Alternator to ensure an AGM battery gets the 14.8v it needs to charge fast and properly? 

If you read our page on How Does a Battery Work, you will find a Paper from a battery expert, described as his 'Lifetime work', where thousands of batteries were analysed over many years. 

This chart below is an extract from the report -

The chart shows that 33% of VRLA batteries, like AGM/Gel batteries, failed from drying out  : That is 33% of all VRLA's evaluated (AGM and Gel) lost enough fluid to destroy the battery. This for a battery where the marketing retailers falsely stress the point they 'don't' Gas or lose any fluid.
Also bear in mind that the batteries in the survey were not only on optimised chargers, but were very expensive, high quality AGM's. These are very different and superior to the much lower quality and cost AGM's available in the Motorhome market place.

Clearly an AGM used in a typical Motorhome may not only lose fluid, but lose capacity due to the fluid loss and that loss may eventually cause premature failure. The last two failed AGM batteries we cut open had lost close on 30% of their fluid at 2 years of age. 

AGM batteries are also more prone to thermal runaway than Wet Acid batteries This is a condition when the battery breaks down and gets hot, the heat promotes the breakdown so the battery gets even hotter. The battery then breaks down faster, producing more heat, so breaks down even faster, this produces more heat, etc. 
As the battery breaks up internally, the resulting debris can then block the pressure/safety valve.
The end result is sometimes battery explosion or fire. 

Have a look at the NCC Verified battery scheme, see : 
Although the scheme lists a number of AGM batteries, nowhere does it state that AGM batteries require a specilaist AGM charge profile rarely found on Motorhomes and almost NEVER on Caravans.

The scheme specifically proposes AGM batteries for Motormover equipped Caravans without any regard for the charger that is likely to be installed, when many may be 13.5v low current chargers. 
Yet the scheme states, "buying an NCC Verified Leisure Battery gives consumers confidence that the battery they purchase for use is fit for purpose". 
The NCC seem to be promoting the most expensive batteries that will then have the shortest lives. 
As though the NCC  are working at helping the Industry that funds them?  

Banner Batteries were the only company warning on their website that an AGM Battery should not be retro fitted to a Motorhome or Caravan that did not have one when new. 
But retailers don't seem to be passing the information on.
Nor is the NCC verified scheme.


Can a Wet battery really have more Charge/discharge cycles than AGM? 

Even if you ignore all the above, the pennies just don't add up when it comes to AGM. 

£ for £ a Yuasa L36-EFB battery will out perform an AGM battery in almost every area, even outperforming an AGM on cycle life. 

An AGM might have nearly double the cycle life on paper, but then it costs twice as much.  £ for £ you can buy two Yuasa L36-EFB's for the price of one AGM. Two L36-EFB's, used one after the other, will supply 460 REAL cycles versus an AGM's 350 'claimed' cycles.

Example : According to the NCC Battery verification web site, a Banner AGM of the same physical size delivers 350 cycles at a cost of around £210, versus the Yuasa L36-EFB  230 cycles at about £105.


So for a similar £210 expenditure you could run two Yuasa L36-EFB's, one after the other, for longer overall life than the cost of a single AGM. That actually makes the two Yuasa's more cost effective at 460 cycles vs the AGM's 350 cycles. 110 more cycles for the same money, and that assumes that the AGM will perform at it's best for the same £210, which history has shown it won't. 

Not only does the L36-EFB last longer, but most of those cycles would be more usable, without any of the limitations of an AGM battery.

Or, to look at it another way

For almost the same £210 you could install two Varta LFD90's coupled together and discharge each battery to just 25% Depth Of Discharge (DOD) vs a single 90Ah AGM discharged to 50%, to withdraw the same usable 45Ah. 

A battery discharged to just 25% DOD will have more than twice the cycle life compared to a single battery discharged to 50% DOD, so a pair of Varta/Bosch Powerframes used in this way will deliver nearly 500 cycles, out performing the AGM's 350 cycles by a huge margin. 

The Varta solution would also be a more flexible 180Ah setup where, in an emergency, you could draw up to 90Ah.

Obviously taking the same 90Ah out of a single 90Ah rated AGM would severely shorten it's life.

In monetary terms, the AGM's claimed extra cycles over Wet Acid is misleading. 

In real World use a Yuasa L36-EFB or Varta/Bosch Powerframe battery will outperform an AGM, even on cycle life.

If all that is true, why are Motorhome manufacturers fitting AGM batteries as standard?

AGM batteries have a long shelf life, old fashioned 'conventional' Wet Acid batteries don't. A conventional Wet battery can discharge on the shelf to debilitating levels inside 3 months.

When a Motorhome can be sat on a Dealers forecourt for many months, that is a big annual cost in replacement wet batteries and subsequent damage to the charging systems. 


Secondly, if an  AGM battery does show discharge at the Factory/Dealers, it can usually be recharged with less obvious signs of trauma, at least initially. 

That applies to AGM batteries in the storeroom as well as the forecourt.

The AGM battery might cost a little more upfront, but that cost is passed on to the customer. The convenience to the Manufacturer of installing the perfect battery for them, costs them nothing.

A bit of History on the Leisure battery chargers installed in Caravan and Motorhome's

If you think the reason that 99% of british Motorhomes and Caravans failure to have an AGM optimised charger is historical, with old fashioned, outdated chargers still in old vehicles from yesteryear, you would be wrong. 

Even the latest offerings from Sargent don't comply with the minimum stated spec of the big AGM battery manufacturers for even half reasonable AGM battery performance or life.

Yes it is true that chargers of 13.5v - 13.8v dominated for most British built Caravans and Motorhomes up to about 2004. Chargers like those from Zig, Plug In Systems, BCA, etc were almost all 13.5v - 13.8v fixed output chargers, fitted in Swift's, Lunars, Coachman's, Elddis etc. 

The BCA/Powerpart unit alone is probably fitted in more UK Caravans than any other unit in the 'modern' British age. They were even being used in new Eldiss motorhomes up to a couple of years ago.

It is still on sale now and popular as a replacement for another manufacturers failed factory original. Yet it has a weak 10amp/13.8v specification not suited to an 80Ah caravan battery on permanent mains hook up, let alone a free camping Motorhome's 160Ah AGM battery bank. 

Around the year 2005'ish Swift starting installing Nordelettronica NE143, multi stage chargers that were probably the first real battery chargers used by a main stream UK builder. With a peak 14.4v output, they revolutionised charging times. 

An indication of just how 'backward' the UK industry is, despite being designed nearly 15 years ago, the Nordelettronica units are STILL amongst the most advanced in the sector. 

Sadly even the latest Nordelettronica UK spec charger version introduced in 2016 doesn't have an AGM charge profile. 

But it has gained a charging profile for Gel, which incredibly, was a milestone for the UK market as Gel charging profiles are almost as rare as AGM. 

Both the latest Sargent 151 with it's fixed, single 13.8v output and the EC600 with it's peak 14.4v wet acid battery output, were released in the last 2 years. 

That's right, the Sargent EC151, a '1980's specification' charger, with a fixed 13.8v, weak 10amp output was released in 2017. 

Incredibly, the Sargent 151 is one of the best selling after market chargers in the UK.

These are recent introductions, yet most definitely not modern, still no AGM charge profile. 

Even in 2018, few main stream UK built Caravans/Motorhome's have even a Gel profile, let alone AGM.  

The Sargent manuals state the chargers are "compatible with AGM batteries" which clearly isn't the way the battery manufacturers see it. Every topline AGM Leisure battery battery manufacturer insists on a minimum 14.8v and Victron Energy suggest 14.9v gets longer life and a fuller charged battery. We have seen AGM's on a Sargent 151 that won't achieve 80% capacity, even after charging for days, just as you might expect.  

Clearly Sargent don't have it right, but then a disparity between the Sargent manual's version of what is good for a battery and that of the battery manufacturers has arisen before. 

The Sargent manuals speak of a feature that shuts down the system when it drops below 9.0v - " protect the battery from severe damage".

I think every battery expert in the country would say that severe battery damage had already occurred at 11v!!! Yuasa, and all other manufacturers, state that for maximum battery life, a Lead battery should not be discharged below 50% Depth Of Discharge (DOD). For a modern battery that is between 12.5 and 12.2v depending on the Technology in the battery, as this affects the battery voltage. 

Again the industry say a Leisure battery can be discharged lower than 50% DOD in an emergency, but 12v should be regarded as a fully discharged battery. Dropping below this level is acknowledged to severely shorten lifetime. Even a Gel battery which is designed to discharge below 80% will have 30% knocked off it's life if that is actually done.

When Yuasa regard a modern technology battery as being full at 13v, 50% discharged at 12.5v and fully discharged at 12.0v, you can see how far away the Sargent manual is from the manufacturers advice.

It isn't just a minor anomaly either, the industry say we should regard 50% DOD as 'fully discharged' for all intents and purposes which is about 12.2v, so Sargents '9.0v' is madness. 

There was a brief glimmer of technological enlighenment with the introduction of the Dutch built Sargent EC325 charger which boosted the voltage of the charger to up to 18v, if it thought the battery needed fast charging. Very clever, very well made unit.

But while a tolerant Wet acid battery would accept that, as shown by the Ford Silver wet batteries that survive for years on a peak 16v charge, 18v would destroy a Gel or AGM Leisure battery in months.   

The Motorhomes built on the continent are altogether different.

The likes of Hymer, Burstner, Frankia, Pilote, Knaus, CI, etc. had a higher technological approach to battery charging in a Motorhome.

For example, it was normal as far back as 1999 for a continental built vehicle to have inbuilt automatic charging of the Starter battery as well as the Leisure battery when on mains EHU. 

Even in 2018, some UK built Motorhomes still require manual selection of charging either the Starter battery or the habitation area battery, but not both at the same time. The latest 'new for 2017' Sargent EC600 has manual switching between Starter and Habitation area battery.

Multi stage fast charging become common on european vehicles from around 2001.

Most Continental vehicles had a Gel charging program as well as Wet Acid, as far back as 2002.

AGM charging profiles were introduced by Hymer around 2015/2016. Their new Solar Regulator got AGM optimised charging at the same time.

The rest of Europe began options of AGM charging profiles around 2016/2017. Some have never offered an AGM option, correctly believing that Gel batteries are a more 'durable' option.

As an overall percentage of the UK Caravan and Motorhome market, the chargers with an AGM profile is very, very small. 

We would guess at less than 0.1%.

One other major company that recognises how poor Motorhome/Caravan chargers can be, is RoadPro, the biggest Motorhome and Caravan specific Leisure battery retailer in the UK.

They state on their Banner Batteries Information web page, also see the document below extracted from the Roadpro web site 08th August 2018, that  most standard chargers are so poor they -

"... will only charge the battery to 80% – 85% of its maximum capacity".

The full text at the top of page 4, states - 

"If you have a 100Ah battery and use 30 Amps, unless you are using an advanced charging system on your vehicle, you’ll probably end up with a battery that’s only half full. This is because most chargers built into vehicles will only charge the battery to 80% – 85% of its maximum capacity". 

Click on the document below for more :

Given that RoadPro accept that standard chargers on "most" Motorhomes and Caravans won't charge a standard battery properly, isn't it strange that they then advocate a battery, that in their own words requires a specialist AGM "14.8v charger"?


Now that AGM batteries have been shown to be a poor performer and EFB have been crowned the new 'King', I wouldn't expect that percentage to alter much.

See this press release below on the Varta Enhanced Flooded Battery, which differs from the standard Powerframe ONLY in having a Polyester scrim on the grid :

Note the text above that states it is "Absolutely maintenance free and Leak Proof". "Evaporated liquid remains inside the battery". 
They are more Gas tight and safer inside the habitation area than even Gel or AGM, which can and do Gas off fluid. 
So on that point :   

The Myth that VRLA batteries (AGM and Gel) are gas tight is exploded here :
If you look at the document below, supplied by Concorde on it's range of top flight AGM batteries, you will see Chapter 6 contains warnings about the dangers of gassing from all VRLA/AGM batteries, not just their own. 

Also look at the Warning on page 21 "because significant amounts of Hydrogen gases may be released from the battery"

So not only do AGM VRLA batteries lose fluid, but when voltages, and especially temperatures, get a bit high, that turns to significant levels of Danger.  
Clear, additional evidence that VRLA batteries are not 'the Gas tight batteries' we are being led to believe.

The battery retailers might be telling us they are 'Gas free', but the manufacturers are telling a different tale.

Please do not fit Gel or AGM batteries inside the habitation area of a Motorhome unless there is a vent pipe to the outside OR you fully understand the risks. 

As it says in the Concorde document, NEVER install a VRLA battery inside a sealed container. That might mean thinking carefully about battery lockers, some of which do not have any venting. 

The Concorde Lifeline battery manual can be found here :

lifeline AGM 1 vs GEL manual.pdf lifeline AGM 1 vs GEL manual.pdf
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