We have a leisure battery in our van with a split charge. However, the battery is now dead and doesn’t hold a charge. I think it’s because when we used it, it got fully drained.

What do i need to ensure a new leisure battery cannot fall below 20%. Is this something I can do myself or is it for an auto electrician?

20% ? If it’s lead acid that’s 50%

You should have a battery level indicator in your van ? Almost all commercial vans do . Often get left out of self builds as folk don’t realise they need them till it’s too late.

Inline volt meter will work but remember it will fluctuate under load and it’s the static number your interested in.

And the expensive answer is solar panels. Roof mounted not the nonsense suitcase ones. – basically a trickle charger that is always there (assuming a quality controller)

If you’re still mid-build my biggest regret is that we didnt add solar.

Fit a decent battery monitor with a shunt to the new battery. Not hard to fit. Victron do a posh one with a Bluetooth link so you can keep an eye on it on your phone from the house.

Remember you only get about 50% of your battery capacity, so size up and I would get a good quality deep cycle lead acid. Best bang for buck for most vans, 140ah gets a good 70ah of usable juice which runs a small camper for a few days.

You could try it on a pulse type charger – something like an Optimate 4 – they can sometimes bring back a dead battery.

We are not mid build but in an ‘improvement phase’. The leisure battery and split charger were installed by a specialist camper van converter when we bought the van (its not a full conversion, just a basic camper) ready for a long trip. Tbh I’m not entirely sure what was fitted. We certainly don’t have a volt meter or battery monitor. Basically the battery would charge up through driving during the day and would get discharged that evening, mainly through use of an electric cool box.

If I buy a new battery, I want to protect it as much as I can.

Would this work?

Not using an electric cool.box would be the best place to start

Secondary is that charging as you drive is not a great way to get your battery charged if it’s done by a basic split charge relay.

Slightly different topic OP but if the main battery user is the fridge (lights and phone charging use very little) then although costly a compressor fridge or coolbox uses massively less power than the solid state sort used in most cool boxes and those little desktop fridges. Worth considering for a long trip if your current cool box isn’t a compressor one.
Our compressor fridge does about weekend on a 90 Ah battery with auto cut out to stop battery damage built into the fridge when I bought it. Using ice packs can extend this.
The other option is a gas fridge but that is a differently complicated beast needing extra vents etc.

1) The most basic verification would be a digital voltmeter (cheap as chips) or you can get a battery monitor with a shunt that will show amps in/out, hours remaining etc. I use a NASA BM-1 but Victron et al have their pricier version.

14.2-14.4 volt – charging
12.7v 100%
12.4v 80%
12.06v 50% (max discharge)

2) Get rid of the thermoelectric coolbox and get a compressor style coolbox (or fridge). Much more efficient, and regulated/thermostat so safer for food storage.

3) Car style leisure batteries are really quite sh!t at their advertised job. Mega expensive trendy Lithium batteries are all the rage but I have two deep cycle 6v golf cart batteries in my van. (Trojan T105’s, two 6v’s in series) 2x 6v 225ahr = 12v 225ahr and you can safely run them to 80% discharge which is 180 usable amps, versus 50% of a 110ahr leisure which is just usable 55 amps. Downside is they are a bit bigger so may not fit where your current battery is located.

4) Don’t underestimate the value of a solar panel, the trickle charge all year round really adds up and essentially makes the batteries maintenance free when you are not consuming lots of power. (keep an eye on battery water levels though)

5) Battery guards…not really looked into those but you might need to use it to switch one or more heavy duty relays to isolate your loads, I imagine its not designed to cope with high loads like fridges and charging devices. You may find it cuts the power prematurely as a load such as a thermoelectric coolbox will pull the battery voltage down, but when it cuts out, the battery voltage will recover somewhat.

Edit: Voltmeters like these, not a handheld unit. (P.S Main voltage is low as it turns out the van goes into hibernate/battery save mode after being switched off for an hour or so…didn’t realise until I fitted these) (PPS The radio runs from the leisure battery which is why its still working)

You might be able to revive the battery with a smart charger? Not too expensive to buy.

I have an electric coolbox. I put prechilled stuff in with ice blocks and run it while driving.
Turn it off once you stop. Just needs to run 45 mins a day to stay cold really.
Helps with the electric consumption