Managing batteries at your leisure

When I noticed recently that my two leisure batteries do not seem to be holding their charge for very long it led me into a whole area that I knew relatively little about. In particular, things proved not to be as simple as I was anticipating.

For context, my van has a vehicle battery to start the engine etc. and two large leisure batteries under a back seat.

Leisure power

One of the first things I discovered was that leisure batteries are different from vehicle batteries, so replacing a leisure battery isn’t just a matter of popping along to the nearest vehicle components shop and buying any old battery.

The vehicle battery has to deliver a surge of power to start the engine and is then quickly topped up again when the engine is running. A leisure battery provides a steady flow of power to the 12V appliances in use – lights, water pump etc.

Thus the leisure battery is drained gradually and then, typically, re-charged from a relatively low condition. This means it has to cope with repeated discharging followed by lengthy re-charging – known as deep cycling.

To vent or not to vent

Vent tube

I was already aware that some batteries are sealed and some can (and should) be opened and topped up with deionised water as they age. I hadn’t realised, however, that unsealed batteries need to be ‘vented’ to remove gases that build up inside.

If the battery is in the engine compartment there’s no problem because the gases (hydrogen and oxygen) can just leave the battery through a small hole in the side, and go straight outside. But when these are leisure batteries inside the living area of the motorhome there can be a potentially explosive build-up of gases. It’s therefore necessary to run a tube from the gas escape vent on the battery to the outside – though some battery compartments may have ventilation built-in.

Vent connection on battery

Strangely, one of my leisure batteries was vented using a tube through the bottom of the van, but the other wasn’t. Quick chats with the technical people at Caravan and Motorhome Club and Brownhills (where I bought the van) confirmed that both should be vented.

That led me on a hunt for plastic tubing of the right diameter, with a connector so that I could vent both batteries through the same hole in the floor. Eventually found what I needed on eBay.

Matching pairs

I also discovered that where there are two leisure batteries they should be the same make and model. Mine weren’t – they were from different manufacturers (1 x Halfords and 1 x Banner) and had different capacities.

There are other makes available, though, and the National Caravan Council has a ‘Verified Leisure Battery Scheme’ to help people select the best battery for them.

I therefore had to decide whether to replace one with a matching battery or start from scratch and get two new ones. At over £100 each I decided to initially try replacing one of them to see if that improved matters.

My first instinct was to get another Halfords one, simply on the grounds that I’d heard of them. However, the chats with technical people referred to above changed my mind. Both said that Banner had outperformed other brands in various independent tests.

So I now have a new Banner battery on its way, as is the plastic tubing, and will see what happens – and will update this accordingly.

Some other useful tips I found

Check the electrolyte levels (that’s the liquid inside the battery) of unsealed batteries regularly by removing the cell covers on top of the battery and looking to see if the liquid level covers the lead plates inside. If it doesn’t, top up with deionised water until it does).

Wear safety glasses when opening the cells and topping up in case of splashing as the electrolyte liquid also contains sulphuric acid.

Try to avoid running the battery until its flat as it probably won’t recover its full capacity. If you have a control panel in the van it may indicate the capacity of the leisure batteries so you know when to re-charge (mine sounds a warning and provides a flashing alarm at 50% capacity – 12.4V).

If you have a solar panel it will probably be configured to maintain a trickle charge to the leisure battery(ies). However, this will depend on the size of the solar panel as a large one could result in over-charging if not properly regulated. My instinct is to leave this kind of thing to experts but there is information online for gifted DIYers.

Carbon monoxide alarms (every van should have one) may also respond to hydrogen, so if you keep getting false alarms it may be responding to hydrogen leaking from a leisure battery and should prompt some investigation.