12V Guru – Is AGM Battery Maintenance Free?

Question to 12V Guru: Is AGM battery maintenance free?

Dear David,

I have recently read with great interest your article regarding battery placement in caravans and a subsequent response to the article submitted by “Alan L” and printed in the Caravan World Magazine.

I note with particular interest your comments that the care and maintenance of the batteries is a serious issue and I totally agree with such comments. The battery issue I have personally experienced and would like to share was similar in description to your comments regarding a split battery case which I shall now expand upon.

Story of the premature battery case splitting

Background: van storage

Our Van is stored at our residence, under full cover and has power supplied at all times. The van may sit for several months at a time between trips. The battery charger is a Ctek unit maintaining the two 100AH maintenance free AGM batteries located in the front boot and housed in standard plastic battery cases.

The batteries were installed in June, 2015 and the charge system / batteries are monitored through a visual display unit located in the front boot. One battery failed in June 2016 and was replaced under warranty. At the time of the replacement the battery case exhibited signs of case expansion however, the case had not split open.

Trip to Bundaberg

Continuing, as time permitted we took the opportunity to travel to Bundaberg, QLD. Upon arrival we noted that the battery monitor reported full charge however, the boot area seemed rather warm. That night the LED lighting started to dim which was most unusual. The following morning I removed the battery box covers, visually inspected the batteries / wiring and connections and all seemed fine. The charge indicator suggested correct charging was in progress.

Failed batteries

That night, again the lights started to dim. The following morning the battery box covers were removed and all seemed fine however, with the aid of a torch light inside the battery boxes it was noted that the side wall of one of the batteries appeared to have expanded. Upon a more detailed inspection I noted that the side wall of one battery had in fact expanded to the stage that the case had actually split open. Upon removal of the batteries it became very clear that one battery had totally failed and further, that the split had occurred sometime earlier as the base of the battery box was totally dry.

I then removed both batteries and took them into the suppliers local agent (Battery World) and requested assistance. The agent professionally advised (as expected) that the failed unit was out of the terms of warranty. We were further advised that the particular product in question (Ultimate Battery) had been known to suffer premature case splitting.

As required we then purchased and installed two new batteries (different manufacturer). We then forwarded correspondence to the Suppliers Head Office regarding the matter and suggested that unit had suffered premature failure due a design fault, however Battery World chose to ignore the correspondence which we considered rather arrogant.

Conclusion. AGM battery: maintenance required

The point of this correspondence is that while batteries may be sold as maintenance free items, and given that many owners performing periodical inspections on a regular basis may detect the obvious signs of a potential problem, the real problem with batteries is that they are usually housed within a battery box and installed in difficult positions at best, which with a “cursory inspection” makes it very hard to see any potential problems at their early stage. Detailed inspections on a regular basis may avert potential problem/s and the additional associated personal stress, particularly if found while travelling.


Ian L


12V Guru answers:


Hi Ian,

Tough situation. It appears you have done everything correctly however the charger and batteries have certainly failed you.

Maintenance free concept

To respond to your last paragraph first regarding regular inspection and AGM battery maintenance. Generally, when we are travelling, we come across many who really don’t pay attention to their rig upfront or the one being towed and just expect to be able to jump in, hitch up and drive off on an event free adventure.

As you recommend, if one is not that experienced at being able to detect and identify general potential problems than suitably qualified caravan and RV repairers with good reputations abound. In my experience “maintenance free” should be treated with the contempt it deserves – it is market guff! Nothing in this world is maintenance free and if you are looking for a hassle free adventure from the local caravan park to “The Big Lap” you need to be prepared and aware.

Battery Case Splitting – Hazardous Concern

I am concerned about the comments of the sales staff from Battery World where you have been quoted the terminology of “suffer premature case splitting” – there is no such thing! It would imply there is “mature case splitting” – i.e. when all batteries eventually fail, they split. This is not the case as 99% of all batteries die gracefully and don’t expand, but just can’t hold voltage and retire to the recycling depot.

Hazardous concern! You mention the batteries in question suffered from a case splitting- “side wall splitting open”.  If you could see the insides of the battery this would be extremely worrying as it means that harmful acidic chemicals would have spilled into the battery box and most likely have vented toxic fumes.  Sealed lead acid batteries have a built-in vent within the case.

If the case has expanded it means that the battery was trying to vent the buildup of internal gases faster than what the vent would allow. Most likely there was a collapsed cell within the battery, and this “tricked” the charger into continuing to allow the battery to draw current resulting in a chemical reaction which saw the case expand as the gases expanded. Hopefully this was contained to the battery box area and not allowed to infiltrate the living area of the caravan?

Invest in quality batteries and battery chargers

We frequently get the question at BMPRO of how much should you pay for quality product? 

  1. The potential harm to yourself, your family or the environment
  2. How much does the inconvenience of rectifying the situation cost you?
  3. What is the impact on our adventure of a failure?

Our response is normally to do your homework and invest in reputable brands that are proven.

Many chargers out there do not have timed algorithms to protect from collapsing batteries or over voltage. So called “smart chargers” should have this feature but unfortunately many charger brands that describe themselves as “smart” means they have digital componentry but not “smart” algorithms that will protect the battery from this this type of scenario.  Normally the Ctek chargers would be able to detect an issue or prevent from timing out but unfortunately not always the case. 

You mentioned that when not travelling you store your van at home and having power regularly run to it.  Not that it relates to the collapse of the battery but good practice to allow the battery to discharge to a depth of discharge of around 50% at least once every 3-4 months. I guess a simple analogy would be that even though we sit at a desk for say 2-3 hours on the computers and we are “fueled and water” we too should be exercised regular just like a deep cycle battery.

Safe travels,

12V Guru


The article was written for Caravan World Magazine.


AGM battery in a battery box
AGM Battery in a battery box monitored by BMPRO power management system
BatteryCheck mounted to the battery
Battery with a BatteryCheck to monitor State of Health, State of Charge and Voltage of deep cycle battery


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