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Updated : 05/04/2018 

"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.

We created this page 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 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 smal number of Motorhomes, probably in the hundreds, actually have AGM optimised mains chargers capable of 14.8v charging. 

The AGM battery in the photo below is typical of an AGM's charging requirements. It has 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?

For years Wet Acid batteries have been recharged at voltages from the 13.5v of a typical Caravan to the 15v output by Ford Cars and Vans since around 2005, showing how incredibly tolerent Wet Acid batteries are of a wide voltage range without damage.

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

AGM batteries are universally recognised as being the Lead Acid technology that is the most intolerant of anything but the exact charge regime. So you can see that problems are going to result if the best charging rates they will get are between 13.5v and 14.4v. Additionally the current of a charger can be an issue.

Lifeline Motorhome 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 16 amp charge rate across BOTH batteries, so just 8amps PEAK 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 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.
So AGM batteries in Motorhomes continued to have short lives.
Only in 2017 did Hymer begin to address the problem of the vehicles Alternator only being able to charge at a none AGM optimised 14.4v, rather than the necessary 14.8v. 

To back up our assertion that AGM batteries are not suited to Motorhome conditions, 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
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We have copied in below one of many recent email exchanges. 

Note their comment about their AGM batteries losing fluid and gassing.


We publish here an edited email :


Thank you for your reply Allan, 
The trip to Spain with long driving hours revealed a number of issues; 
•the fridge supply cut out on a number of occasions requiring it to be reset.
•the control panel cut out and when reset showed the leisure batteries to be low however if I switched the panel off and on again the batteries seemed to recover very quickly. 
there was a sulphur smell in the van, on investigation I found that the dealer had not fitted a vent pipe to the second battery as was fitted to the original. I have now rectified this. Could the alternator have been overcharging or, probably more likely, the condition of the batteries?
The company xxxxxxxxx fitted a 150 watt solar panel and the second leisure battery for the previous owner, considering the fact that they did not fit a vent and other faults I have found in their workmanship I have little faith in this electrical system.
I would very much like for you to check that this system has been wired correctly.....
Your thoughts please

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 3 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.

Enough evidence to question an AGM's alleged reliability and durability? 

Here is a lot more, but if you are bored skip to the Summary which covers the real cost of an AGM, £ for £. 


Many battery retailers are 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 continous 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 how come a wet acid battery, beat all AGM's to take first place?


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 1970's. Not the latest and best 'Wet' batteries.

For example, you may read that an AGM battery can be charged faster than a  'conventionial' 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.

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 peformance 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, regardles of what the marketing hype indicates. 

On an Elddis Motorhome's 13.8v charger 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 voltage drop) 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. This in turn means it will take longer to charge for the next use, so possibly won't get back up to full charge again, etc. suffering damage from inadequate charging and over discharging, etc. 

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 batteiesy 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.
The datasheet below for a Banner AGM 59201 battery shows that the fluid loss is <1 g/Ah. In other words there is fluid loss which goes against what you will generally hear.
Note also that it requires a charging voltage of 14.8v. 
See further down the page for how the charging/discharge current can have a huge impact on an AGM batteries life.

Banner AGM 59201 data sheet.pdf Banner AGM 59201 data sheet.pdf
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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 of the type and cost of Victron batteries. 
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. 

A modern Powerframe Wet batteries tolerance to higher temperatures and varied charging styles is far superior to an AGM's.
The below chart shows how much life can be lost by AGM (and more so Gel) batteries when operated at higher temperatures. 
Just a 10 degree rise at the Plates, knocks a high quality AGM batteries life down from 10 years to 4 years. 
A 20 degree rise at the Plates drops a 10 year life to a meagre 2 years, 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. 
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 continous charge/discharge, raises the Plate temperature into the zone that can decimate AGM/Gel life, as noted above. 
See section 15 :

"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 regularly 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 ideal current in order 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'.

Also, the VMF battery pictured at the top of the page, has a quoted Maximum charge rate of 25a, but the spec sheet suggests 10amps is the ideal for the longest life. It can be charged at 25a but the life could be reduced by as much as 50%. 

Again, that they print this maximum on the casing says a lot about an AGM batteries limitations, it is the battery retailers that are not passing this on to the customers.
We suspect this move towards printing relevant info on the batteries is to overcome that misinformation from the retailers.

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 termperature 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 where many are used in the warmer months or warmer climesAGM batteries are likely to wilt under the Plate temperatures they will operate 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. 


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 the beginning of 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 13v may 'charge' an AGM battery, but it won't charge it necessarily properly or quickly. 

If a chargers advertising blurb states it is 'AGM compliant', but it does not have a separate AGM specific charge profile, e.g. like the Rovert charger range which has only 'Wet' and 'Gel' settings, then the retailer is 'Pulling the Wool over your eyes'.

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 Motorhomes 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.

'Professional' Advice When buying AGM?

We don't know of a single AGM purchaser that has been warned of the requirement for a specialist battery charger at purchase time. In fact the reverse is true, every purchaser we have had feedback from has been informed the battery is suitable without any questions being asked about the Motorhome Electrical architecture. 

So we did a mini survey at 2 Main Motorhome Dealers, a Halfords Store and a big battery retailer. They all said an AGM battery could be fitted in our 'imaginary' Motorhome without asking any questions about the Motorhome age, the charger technology or the Alternator. 

When we then said the charger had a fixed output with no AGM charge profile, they all still said an AGM battery was fine. Yet the battery manufacturers say it isn't.

Again when we asked what were the advantages of spending twice as much money on an AGM battery, all we got was 'they are better'. Not one of them could tell us the advantages or disadvantages of AGM when used in a Motorhome

Don't believe that? 
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". 

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.

So I guess when the NCC gets it so wrong, we can forgive Halfords.


More Charge/Discharge cycles from a Wet battery 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. 

This would also be a more flexible 180Ah setup where, in an emergency, you could draw up to 90Ah down to a 50% DOD discharge.

Obviously taking the same 90Ah out of a single 90Ah rated AGM would severely shorten it's life down to about 60 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 even outperform an AGM on cycle life.

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

Lead Acid Gel and 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.

A good AGM and Gel battery has a quoted shelf life of at least 6 months, some 12 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.


The BMW car we mentioned above that suffered failure of it's Stop Start battery in less than three years, went back to the BMW Dealer who then fitted, not another AGM battery, but a Varta/Bosch Enhanced Flooded Powerframe Wet Acid Battery. 

These batteries (the same that won the Truck battery of the Year as also mentioned above) have recently been approved for use in Stop Start applications and seemingly able to outperform AGM in those applications due to their better heat tolerance. 

The EFB version of the Powerframe battery  that we have been saying is the best going, is even better, and now officially better than AGM!!!

Well, in the eyes of one BMW Dealer anyway.

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? 

It is also a 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
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