Charging a caravan battery

I have normally left the caravan battery in the caravan and caravan plugged in so battery is maintained, likely best idea in summer when used a lot and the motor mover has been used to park it up.

However over winter not sure if to leave in caravan or remove and use a small charger in the garage. I know what the charger in the garage is doing, measuring input I see 65W, 52W and 14W which I would think relates to 3.8A, 3A and 0.8A the fourth rate of 0.1A the battery has not been on charge for long enough for charger to drop to it.

In the caravan not a clue what the charger is doing. No idea if pulse, stage, float, or trickle charger and with 16A power lead not easy to measure power being used, it is on my to do list. Caravan in my father-in-laws so not easy to monitor.

So wonder has anyone else looked at caravan battery maintenance and if so what were their results?

Personally I would take it out and use a small maintenance charger to keep it topped up. Something like https://www.amazon.co.uk/AUTOMATIC-BATTERY-TRICKLE-MAINTENANCE-CHARGING/dp/B004VRJD0G

I rather ike the Victron blue power range of small chargers - but they are rather more expensive than the on glblades points at.

ericmark said:

However over winter not sure if to leave in caravan or remove and use a small charger in the garage.

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Or indoors.

Lead acid batteries don't like being cold and idle.

I use one of these, in my case the batteries are from a boat rather than a caravan but the principle is the same, they're 120AH leisure batteries. It would take a long time to recharge from flat but is perfectly fine keeping them on float charge. https://www.optimate.co.uk/products/optimate-2

i don’t know if this is better, but i leave my moho and boat on a timer switch. as the electric on the boat is metered.

pops on for 30 mins a day and has a dehumidifier (boat) which pops on too

Time clock makes sense for automatic unattended operation. What I tend to do is just connect the charger now and again, the batteries won't come to any harm being left for a week or two at a time, or even a month.

If the caravan was in my own house I think the timer is good, but it is not possible to alter supply so would need to be inside the caravan. I have some wiring problems so adding something while sorting it out is the way. Which is why I raised the subject to get some ideas.

The charger I have it seems needs some one to press a button for it to start charging. This means not really much good on a timer or away from home. Pity as cheap and has four stages, I do need to monitor the one built into the caravan.

I bring our caravan battery home over winter, give it a charge bi monthly with an Optimate battery tender (which I also use for my car).

I had intended to produce a chart showing charge rate, first peak was due to using a standard unregulated charger to raise the voltage over the threshold which causes the regulated charger to auto select 12 volt rather than 6 volt, because the battery was heavy sulphated the first 3.8 amp stage was very short, it went to 3 amp very quickly, I had intended to use Photoshop to extend the chart, and to start with it worked. However as it hit the 0.8 amp output which is 14 watt input the scale changed first to 40W and then 20W so can't really link them together.

The battery came out of the old caravan which did not have a motor mover, the place where it is parked has a 13A outlet not 16A so my wife was unable to plug the caravan in as at that time only one hookup lead since then we have two leads one with 16A the other with 13A plugs on them. Since it should switch from 3A to 0.8A at 80% charge and it took 16.5 hours it would seem the battery has lost capacity and is now more like 62 Ah rather than 88 Ah and I have calculated it should have run another 15.5 hours to complete before dropping to 0.1 amp charge, however now run for some 28 hours at 0.8A which seems to point to some recovery of the battery likely due to the low charge rate.

The charger a cheap Lidi one displays voltage it shows 13.7 at this point, the chart with the instructions seems to show at 14.4 volt it will drop to final stage with 0.1 amp charge then it will return to 0.8 amp if voltage drops to 12.8 volt. Without an energy meter drawing a graph I would not know when or if it changes stages, so this is the first time I have been able to see what a charger actually does, unfortunately it needs to be in range of the hub to record and produce a graph so don't know what the caravan charger uses.

As a note this is the second Lidi 3.8 amp charger I have owned, at first the first one which did not show voltage seemed to work well, it was bought to recharge my mothers wheel chair but when the car boot was left open tried to use it to charge car battery, the problem is these chargers consider under 7.5 volt is a 6 volt battery so needed to boost the battery a little first, I connected a 12 amp charger at same time as the 3.8 amp and this caused the 3.8 amp charger to fail, I note a change now in the instructions the new one has an over voltage cut out it was not in the old one. Considering it was my fault old one failed I bought the new one, however could not get it to charge the wheel chair battery, not wanting to blow the new one same way as old one did not want to connect with another charger to get it started, and the small VRLA in the wheel chair is too small to stick a 12 amp charger on it and leave, so hope is once the caravan battery is charged I can connect the two batteries in parallel and maybe recover the wheel chair battery which the Lidi charger was bought to charge.

However once I realised how discharged the old caravan battery was, it got me wondering about the new one, the old one was really there just to stabilise the charger output and take the surge as water pump was used, however the new one has a motor mover and weighs more so really we need the mover to get it up the drive, I would reverse old one into the gate way, but new one also longer, so would be hard, so in short now the battery is important.

The old one was clearly charged every time the caravan was on a site, and is used Feb to Nov so the battery should not have been discharged. So now I need to look after the battery better. There is a fault with the relays in the new caravan I noted fuses across the in and out where clearly a relay has failed, so I need to do some work, not sure what the relays do, I assume some change over from power from car to power from mains hookup. We at this time do not have any charging from car.

I looked at a charger from car and at around £200 seems a bit steep. I was looking at this one not sure if 30 amp too much, but the although Sterling do a range these are even more expensive.

I have considered an inverter in the car stepping up to 230 volt and a battery charger in the caravan, with a 230 volt plug and socket between car and caravan, however already been caught out once, think my inverter is around 120W so taking mother on holiday I plugged in the battery charger for her mobility scooter and all seemed to work, until she used the scooter and the charger output went up, then it failed. However step up then down again does seem a cheaper option, removes need for heavy cables, also no volt drop so seems better option. However easy way is if I can use cig lighter in boot, so limited to 16 amp.

So question is since we always use sites with hook up is it really worth the effort? Did consider the Lidi charger and existing inverter, however at 48 hours to charge, can't think of a caravan site that far away?

How about Plan B: Don't use a lead-acid battery?

Optimate 4 is £65 and you can use it for caravan/ car/ motorbikes etc.

Step up to 240v then back down to 12v is a very inefficient way to go!.

I'm sure our car charges the caravan battery through the hookup while towing, through the switched 12v supply pin..

Keithmac said:

Optimate 4 is £65 and you can use it for caravan/ car/ motorbikes etc.

Step up to 240v then back down to 12v is a very inefficient way to go!.

I'm sure our car charges the caravan battery through the hookup while towing, through the switched 12v supply pin..

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Charges at 0.8A, 0.5A and 0.2, at £68 Lidi Ultimate Speed 3.8A, 3A, 0.8A, 0.1A at £14 the CTek is likely the most well know of the small chargers designed to recover lead acid batteries as will as the simple charging they do a range 0.8A, 3.8A, 5A and much larger models, the MSX 3.8 is 7 stage and costs around £66 clearly a lot better quality than the cheap Lidi.

However I am into day 3 charging with the cheap Lidi charger and so I would say for a caravan battery really too small, simple maths 3.8A the 0.8A pulse from 7.5 to 10.5 volt can't really be quantified and although it says it drops from 3.8A to 3A at 12.8 volt it does not give it as a percent of charge but graph shows around 40% and when it hits 80% it does drop to 0.8A so with a 88 AH battery if I assume it charges at 3.8A for first 80% it will take 40½ hours, at 3A it will take 45½ hours before going to maintain mode.

The OptiMate 4 has a 1A charge max and 48 hours run time max which is clearly why it stated 55 Ah battery max, after 48 hours what ever the state it will drop to 0.2A charge, so taking same battery 88 Ah after 48 hours there is 40 Ah left so it will take with no losses 248 hours to charge the battery. So in round terms a week and a half to recharge the battery. And this will no loses.

In real terms there are losses, and my cheap Lidi charger at 0.8A does not seem to be raising in voltage, not really surprised the battery is rather old, started Thursday just before 11 am at stage 2 the stage 1 was missed because I gave it a quick boost with a 12A battery charger to get voltage over 7.5 volt so it would see it as a 12 volt battery, it went into stage 3 without me noticing the step on the energy meter just after 3:30 Friday it went into stage 4. So 16.5 hours, at stage 4, the stage 5 is still running at 0.8A started with voltage dropping to 13.2 and now at 13.7 nearly 24 hours latter, as to if it will ever reach 14.4 volt needed to drop into last stage not sure.

As to charging off the car I have been there and done that, even with the second battery in the boot rather than in caravan the split charging relay would give it a boost after first starting maybe 10A but within 5 minutes it was down to 5A and for most of the journey around 2A, stick it in the caravan and in real terms it simply did not charge, OK may get 5A when car first charging but after 10 minutes down to 1A. Taking the three phase supply from alternator did work a bit better, I had two batteries charged that way in the works van with a 12/24 volt change over link and I used it to jump start wagons. But unlikely to find that in a private car.

So in real terms my 100 watt inverter and the Lidi battery charger plugged into that would recharge the battery quicker than the split charging relay. However as said 16.5 hours to get 80% charged, I do not tow a caravan for that long, not only caravans narrow boats have same problem, maybe cruse for 7 hours a day but even with twin 70A alternators one for engine battery and one for domestic battery it could not put back in what had been drained over night. With a caravan 30A is about max so in real terms all split charging does is extend how long before the battery is fully discharged it will not keep up.

The little generator throbbing away all day long is a pain, however it really is the only way one can run a caravan without mains hook up for an extended time, split charging and solar panels only extend how long before you need either a mains hook up or run generator. Main reason for not having mains hook up is in the summer it is expensive, in the winter so few use the sites no problem getting mains hook up for reasonable cost. So whole idea of charging from car is to save money, at £200 for a 30A DC/DC inverter plus wiring every time you change the car. We have decided for the moment not to bother, when we are no longer looking after my mum and we can go away for months at a time then it may change, but I think even then an inverter generator is a better option.

I do however thank everyone who answered it helped me work it all out in my head.

For storage something like the Optimate is ideal. For recharging from flat it will do it but only slowly. Mine is the Optimate 2, 0.8A charge rate. I've recharged the digger's 120AH battery from completely flat once, it took several days but got there in the end. By the way for your calculations you should be taking around 50% of the rated battery capacity. A normal leisure battery won't last long if discharged below 50% on a regular basis.

To improve charging in the car, could you fit a smart alternator controller as well as the split charge relay? Or Sterling's alternator to battery charger would be the deluxe solution if it can be accommodated. Both these solutions are really intended for boats.