Translate This Page

Updated : 8/05/2018 

"Hi Allan, Our motorhome is back up and running thanks to your expert help, advise and parts. 
I cannot thank you enough in sorting out this problem and would certainly recommend you in the future. 
Regards, K.M. 4/3/2017".


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

Did you know that AGM batteries have suffered so many failures in real world automotive use that Audi, VW, Seat, Skoda have pulled them out of their cars and are moving back to Wet Acid technology?

The general view in the battery industry is that AGM did not deliver on the 'laboratory' promise.

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.

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 EFB technology. AGM hardly gets a look in. The website actually states that EFB technology is the technology of the moment. See :

The Banner EFB 580 11 stands out in particular, which you will note is listed as Zero fluid loss. Not low fluid loss of some low maintenance batteries, but zero. 

We started this page some years ago because back as far 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 14.7v charging rate for maximum performance and life when almost all the UK Motorhomes/Caravans have at best 14.4v, or even worse a 13.5v charger

We don't know of any Caravans that rolled off the production line up to 2016 with AGM optimised chargers. 

Only a very small number of Motorhomes, probably in the hundreds, actually have AGM optimised mains chargers capable of 14.8v charging. 

The problem of degraded AGM batteries through inadequate charging 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. 

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

As an example of the reverse of that 'particular' requirement by AGM, on their web site Banner Batteries now specifically make the point for their new Wet Acid Leisure battery range, "The suitability of any standard charger makes charging straightforward".  

That has never been printed in the 'specifications' before for a Lead Acid battery. It has always been assumed and taken for granted, but with this new range of Wet and EFB batteries, Banner are working really hard to address the issues with the previous AGM range in Motorhomes and Caravans.

For years Wet Acid batteries have happily tolerated recharge voltages from the 13.5v of a typical Caravan power supply/charger to the 15v output by Ford Cars and Vans since around 2005. But AGM batteries are very fussy, about several factors. 

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 temperature operation.

So AGM need higher charge voltages, but did you know some need a huge 40amp charger for a 200Ah battery bank?

Lifeline Motorhome specific AGM batteries from Concorde, the largest manufacturer of VRLA batteries for commercial and military aircraft, stipulate : For repetitive Deep Cycling, chargers should have an output current of 20amps per 100Ah battery. If the output current is less than this value the cycle life of the battery may be negatively affected.

See the full Lifeline battery document at the end of the webpage.
I suspect you can imagine what will happen if 2 x 100Ah AGM Motorhome habitation batteries get the usual 8 amps per 100Ah battery (that is just 4 amps per battery) PLUS the incorrect voltage? 
I guess in such a case, the term above from Concorde : "battery may be negatively affected" will need to have 'significantly' added to the sentence?

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 early.
As a result Hymer rushed through a charger that did have an AGM optimised voltage setting, but not the ideal high current requirement, but they didn't address the Alternator low charge voltage, which was optimised for Wet Acid.

AGM batteries in Motorhomes continued to have short lives.

As of April 2018 there is still no published strategy for addressing the Alternator issue.
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 from cars, that Hymer 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 ask Victron Energy, the biggest specialist Deep Cycling battery and Charger manufacturer in the World.

Aside from not being adequately charged, which will cover later, AGM batteries have a fine temperature operating window.
Modern Powerframe Wet/EFB batteries tolerance to higher temperatures and varied charging styles is far superior to an AGM.
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.
Remember these batteries shown on the Chart are very, very expensive Victron AGM batteries. Imagine how a much lower cost motorhome AGM will fair, no wonder some consumers don't see the battery last 12 months. See the Victron chart below :

30 degrees is not exactly a surface temperature that is going to burn your hands. The 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 condition environments.

We use Victron Batteries as an example because they are leaders in their class, so any AGM battery behaviour we highlight here is the very best you can expect compared to much lower quality Motorhome or 'Stop Start' AGM  batteries.    

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 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.

We get emails from people with 'proof' that their particular battery, "has a max charge rate of 45amps making what you say nonsense"

There is a big difference between a Max current rating and the manufacturers optimum current to maintain decent battery life. 
You can charge/discharge any battery at any current you like, but you won't get the optimum life.
Battery retailers claim all sorts of extremes to aid sales, some just forget to publish the downside if you go to those 'maximums'.

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. 
Something not one mainsteam motorhome/caravan rolling off the production line upto Feb 2018 had fitted as standard. Not even Hymers that have AGM's fitted at the factory.


The Victron Energy chart below shows that to achieve the best performance from their AGM batteries upto 14.9v is the optimum charge rate.

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.

Victron Energy Battery Datasheet.pdf Victron Energy Battery Datasheet.pdf
Size : 256.391 Kb
Type : pdf

Even though AGM batteries have only been used in Cars for only a short time, being a relatively new technology, the Forums and press are full of prematurely failed AGM batteries in both cars and Motorhomes. The days of an 8 year life, £90 Starter Battery are over, think more like 2 years and £180.

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.


Many battery retailers have been telling us how AGM batteries are the technology for today, out performing everything else.

Yet a high technology 'Wet Acid' battery scooped the "Best Battery In The World" trophy, in the toughest market, Truck batteries? 

Big Trucks these days place an enormous strain on the Batteries, as they do far more than start the engine. Many big Trucks have 'Habitation' areas where the driver will often sleep the night on long journeys. The rear section of the cabs have a dedicated sleeping area, Diesel fuel heater running all night long, TV, lights, stereo, Kettle, Inverters, etc. 

These big Truck batteries have to perform as a Habitation and Starter battery in one, taking quite a hammering during the continuous 300+ days of the year a truck is on the road. 

The load on the battery is probably greater than a Motorhomes, because a Truck battery has the added task of starting a 16,000cc, 600bhp engine. 

So if AGM is the heavy duty option, how come a wet acid battery, beat all AGM's to take first place? Why are all the new big Truck batteries being rolled out with EFB technology? 


The Enhanced high tech Powerframe battery, whose acknowledged quality is clear from taking the award above, should be the benchmark when comparing high technology AGM's. 

Yet the AGM hype is misleading by comparing an AGM's 'advantages' to inferior 'old fashioned high Antimony' battery technology from the 1990's. Not the latest and best 'Wet' Enhanced Flooded Batteries (EFB), sometimes called Advanced Flooded Batteries (AFB) batteries.

For example, you may read that an AGM battery can be charged faster than a  'conventional' wet battery, sometimes referred to as 'greater charge acceptance'. 

Yet comparisons against best of breed modern quality, high tech batteries like the Powerframe Varta LFD/Bosch L5 range, show a different story. 

If you look at the image below, it compares the advantages of the Bosch AGM L6 battery versus the Bosch L5 Wet Acid Deep Cycle battery (identical to the Varta LFD range) : 


You can see that 'Charge acceptance', 2nd from bottom line, is the same 2 star rating for both the highly regarded Wet Acid Powerframe Bosch L5 and the AGM L6. 

The Bosch L5 Wet is made by Johnson Controls on the same production line as their own label Varta LFD90. Same battery just different labels and marketing.

It is universally accepted that the best wet acid EFB technology charges as quickly, or faster, than AGM, but retailers still compare an AGM to 'conventional' wet batteries that went out of favour in the 1990's. 

The majority of Motorhomes and Caravans don't have a 14.7v Alternator or 14.7v mains charger or high current charger so the alleged performance advantages of AGM, which rely on that higher charge voltage to charge 'quickly', are not realised. 

If an AGM is charged with 14.3v it will take longer to charge than a Bosch L5/Varta LFD90, regardless of what the marketing hype indicates. 

On the 13.8v charger fitted in some Elddis 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) then that will further disadvantage an AGM versus a faster charging Powerframe Varta LFD90/Bosch L5, which isn't so fussy about charging voltages. 

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

You may also read that an AGM battery has greater Deep discharge and Cyclic capability than other Lead Acid batteries? This is again misleading, as Gel Lead Acid batteries will Deep Discharge better than most AGM batteries in the same category. 
A Gel battery will cope much better with deep discharges and return more charge/discharge cycles by a significant factor than AGM's aimed at the same market. 
The Victron Energy battery datasheet noted earlier, contains the image below which shows the outstanding Victron Energy's Long Life Gel battery, at 4,500 cycles, outperforming it's Deep Cycle AGM's 1,500 cycles. 
Even the Victron Energy "ordinary" Gel has 2,500 cycles outperforming their AGM version. Few AGM batteries aimed at the Motorhome market achieve 500 cycles, let alone the outstanding Victron Energy Gel batteries 1.500 cycles.  

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 Forum post above and 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. How can dangerous gas possibly build up if it is never released outside the battery?

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 report below is an extract from the report and shows that 33% of VRLA batteries, like AGM/Gel batteries, failed from drying out, as shown in the chart below

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. 
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. 

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 a Varta/Bosch Powerframe battery outperformed a conventional wet acid battery by a ratio of better than 2 : 1 in hot desert conditions.

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 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 are used in the warmer months and/or warmer climes. The conditions that AGM batteries are likely to wilt under. 
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. 

Which brings us back to why the Battery voted 2016 Best for Trucks is not an AGM, but a Wet battery.


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 13.0v 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 AGM specific charge profile, such as the Rovert charger range which has only '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? 


Stop Start cars with AGM batteries are matched by Smart ECU controlled Alternators with voltages from a 13.5 'trickle' to over 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? 

This isn't just about mains 230v chargers, it is all charging systems from Alternator to Solar. 

If AGM batteries are fitted, to get the best from the battery the charging systems need to match, otherwise the batteries will under perform, potentially to a level lower than the cheapest budget batteries.

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. To us that seems like the NCC are not working towards helping the consumers, but 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 Varta LFD90/Bosch L5 Powerframe 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 Varta LFD 90's for the price of one AGM. Two LFD90's, used one after the other, will supply 400 REAL cycles versus an AGM's 350 'alleged' 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 £190, versus the Varta LFD 90/Bosch L5's  200 cycles at £91 (prices August 2017). 

So for a similar £190 expenditure you could run two Varta LFD90's, one after the other, for longer overall life than the cost of a single AGM. That actually makes the two Vartas more cost effective at 400 cycles vs the AGM's 350 cycles for the same £190. 

Not only is the Powerframe Varta longer lasting and more cost effective, but with upto to 70% better electrical flow from the BoschL5/Varta LFD90 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 £190 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 solaution 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 down to a handful of cycles.

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

In real World use a Varta/Bosch Powerframe battery like the Varta LFD90 or Bosch L5 will outperform an AGM, even on cycle life.

If all that is correct, 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 2 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.

I guess the full Stop/Start approval rating of the EFB version of Powerframe by Varta implies it is interchangeable with an AGM battery, on an AGM charging system? 

That suggests it will happily take an AGM's 14.8 volts without damage. 

If that is so, a Powerframe that is fast charging on 14.4v, will maybe become Turbo'Charged' on the 14.8v AGM voltage with incredibly short recharge times without affecting it's life? 

Not something we suggest you try, but it is testament to just how rugged and durable the Powerframe technology is.

See this press release below on the 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
Size : 1817.495 Kb
Type : pdf


We welcome all feedback, good and bad.

See the Contact Us page for contact details.

Steca style Solar 30.pdf Steca style Solar 30.pdf
Size : 615.338 Kb
Type : pdf