Motorhome Leisure Battery Drain? Causes and Cures
What would cause your leisure battery to drain?
The main causes of battery drain is a faulty leisure battery. The battery may be old, cold or just need to be replaced. A faulty piece of equipment such as the charger or anything connected to the leisure battery could cause a drain.
This blog takes a look at some of the problems we had. The diagnosis of what is causing a battery drain can be difficult to work out. By taking some simple methodical steps you can usually find the battery draining culprit.
Most of the information is based on wet lead-acid batteries as those are the type I use in my motorhome and they tend to be a bit cheaper than other types.
For an explanation of the different types of leisure battery – see here.
Causes of Leisure Battery Drain?
There are many reasons battery drain occurs in a motorhome. The main ones being;
Faulty Leisure Battery
This tends to be the main problem. If your battery is very old – more than 5 years would be considered old, although I personally would use the battery as long as possible. They are not cheap to replace and I like to squeeze as much as possible out of them.
A battery can fail for a number of reasons
Age of the Battery
There are only so many years that a battery will work for. Generally, around 5 to 7 years if you really look after your battery and have a good charger, it may even last longer. If you have a cheap charger and let it run flat a lot you probably won\’t even get to 5 years. These ages are for a typical lead-acid battery, AGM (Absorbent Glass Mat) batteries are about the same.
Extreme cold is very bad for a battery. A fully charged battery can survive much lower temperatures than a poorly charged battery approximately -50℃ (-58℉) for a fully charged and -1℃ (30℉) for a flat battery. So make sure your batteries are fully charged in the winter. A battery will not recover from being frozen.
Inadequately Charged Battery
The charger is very important. If your battery is not charged properly each time then it will radically shorten the life of your battery. This tends to be what people underrate. The charger is every bit as important as the battery. If you buy a really expensive battery and use a really cheap charger the chances are the life of the battery will be shortened.
This is especially true if you tend to run your batteries until they are flat. Once they reach the 12volt mark they are flat and you should not use it anymore as damage will occur. There are some devices that you can buy which will protect the battery by cutting it off once the voltage reaches a certain level. They can be a pain as your power just cuts off abruptly but they do protect your expensive batteries so worth it.
To charge from 12 volts or below you really need a smart charger that will adjust the current to bring it back to a charged state. They will charge it in such a way as to reduce any internal damage that may occur.
Some of the cheaper chargers have such small current ratings that they may never be able to charge your leisure battery. Most of the recommendations I have read is that you should have a charger that is able to charge at a rate of at least 10% of your total amp hours. So if you have a battery set up of just one battery at 110Ah you will need a charger that can charge at a rate of 11A. If you have a double battery set up your charger will have to be able to charge at 22A. At this power, the charger will be able to charge the battery quickly and recondition the battery as well – assuming you are using a smart charger.
Spend time choosing a charger and get the best one you can afford.
Battery Left in a Discharged State
It is very bad for a battery to be left in a discharged state, that is, left to go flat and not charged. The battery cells quickly degrade in this state and is sometimes not recoverable. The battery cells suffer from something called sulphation when they are let go flat and this will greatly reduce the life of the battery.
A Light Left on or Other Hidden Loads
Not just a light but there are a whole number of electrical devices and items that consume power in a motorhome. Even things like signal boosters and amps can be a problem as these things are generally out of sight and forgotten about. Get to know your motorhome and check out all the items connected to the power and work out if you need them.
We had a load of old boxes connected to the power that were not required any more, such as aerial boosters for ariels that are not in use, tv signal booster that didn\’t work but was still consuming power. It was amazing what people had kept connected to the battery and never used, these were relics from the 1990s. All these little devices suck the power out of your battery.
Inverter Left On
This is a favourite of ours. The inverter switch is near the floor and very easy to brush by and switch on the inverter. There is only a tiny light to let you know and even though we have never used it the battery has gone flat within a few days of being left on. A bit of a nuisance. Make sure your inverter is off if not in use as it may still be consuming power.
As motorhomes age so do the electrical connections. I have spent hours replacing connections and even some cable. If the connections get we they will corrode and will cause various types of faults. Whenever you find one fix it straight away or you will spend hours at some point in the future trying to find a fault that takes a few minutes to fix.
Always check the earthing cables that go onto the body of the motorhome, these are also a favourite place for corrosion and poor connections.
Years of Electrical Alterations
This can be a real pain. Sometimes to find a fault you have to trace a cable from the battery to wherever it goes just to find out what it does. When additions are made to a motorhome they can be wired directly from the battery rather than through the fuse box. This means that these new additions won\’t be isolated by the master switch and can make the process of fault finding take a lot more time.
There is no easy way to do this but a cheap multimeter will come in very handy. You will also need a lot of time.
Very Cold Weather
The amount of power a battery has is measured at 25℃ (77℉). For each 1℃ (1.8℉) the temperature drops the efficiency of the battery drops by 1%.
So if you have a 100ah battery and the temperature is 0℃ the battery will operate like a 75ah battery, you basically lose 25% capacity.
This is very significant in very cold countries. Your battery can be greatly affected by temperature and if the battery is old then the effect is even greater. This is why, especially here in Scotland, a lot of batteries fail in the winter time.
I was shocked when I found this out, a lot of the time it can be -5℃ here – that\’s a 30% drop in battery capacity.
The Radio – Especially if Newly Fitted
A lot of new radios will have a power draw so they can keep settings in the memory or have their lights on so you can find the power switch.
The radio in our motorhome would have been wired through the ignition switch and would only come on when the engine was on or the ignition on. As I like to listen to music while we are camped I wired the stereo to the leisure battery rather than the starter battery. This helps to protect the starter battery but will draw a constant current from the leisure battery. Doing this helps to protect the starter battery from being depleted and leaving you stranded somewhere.
Our new radio has a constant light on which is a real nuisance, however, removal of the facia plate cuts all the power. If your stereo has a removable facia try that and see if it cuts all power usage.
Defective Charge Relay?
It is possible for the split charge relay to become stuck and you would have the starter battery connected to the leisure battery. Not a huge problem and you were not in a campsite for some time. You would only notice when you have drained your leisure battery and find that the motorhome won’t start. This would give the impression of having a faulty starter battery.
Tracking Down the Cause of a Battery Drain
This is by no means a complete guide but may point you in the right direction.
The best way to track down an electrical fault is to work in a logical fashion. You will need a lot of patience and a multimeter. The first step is to;
Start at the Battery.
First of all, make sure all the connections are good. Look for any corrosion or loose fittings and connectors. All the cables should look nice and clean with connectors tightly fitting – they should not come away with the slightest tug. If you are happy that the battery terminals are good then;
Disconnect the battery and take a reading of the voltage.
If the reading is low charge the battery with an external charger if you have one, otherwise you will have to charge the battery on hook up.
See if the battery holds a charge, try and give it a day or two to make sure it\’s going to hold any charge. If it seems to lose charge then you may have a faulty battery.
If you determine that the battery is good and the battery is holding a charge then refit the battery and move onto the next step.
Switch off the Power for the Habitation Side of the Motorhome.
There will be a main switch for your van that will switch off everything that is connected to the motorhome leisure battery, at least that is the theory.
If your motorhome is any age at all you may find that there are a few additions or modifications that actually bypass this switch.
So you want to determine if there is anything in the motorhome that will be using power when the main switch is off.
You can use a meter to see if there is any power usage or if you have a good power meter in your motorhome this will also be able to let you know. If you don\’t have a meter then it\’s a waiting game to see if your battery is being used by something. Give it a few days and you should be able to see. By switching the main switch off you cut out all the appliances that are powered through the fuse box. If the battery is not showing a drain you know its problem with something that\’s powered through the fuse box. If it still shows a drain then its something that has been fitted later and does not go through the fuse box. Simple.
If the battery holds its charge then the drain is something that is powered through the fuse box.
Next stage is to check the fuse box. Take a photo of your fuse box and pull out all the fuses. Put them in one by one until you find which circuit in the motorhome is causing the power drain. Either measure the current of each circuit with a multimeter as you put the fuses back in or keep an eye on the meter at the motorhome control panel if you have one.
Usually, there are about 10 fuses.
In our older motorhome, we have really ancient fuses, the type before the blade fuses. These sometimes need a little rub with sandpaper on the fuse and the fuse holder to freshen up the connection.
Once you determine what is on the problem circuit then it should be relatively easy to fix from there. Just see what that particular circuit is running and you should be able to narrow down to the offending item.
Personal Battery Problems so Far
In our motorhome the leisure battery had a second battery in parallel so should be adding power to the leisure side of the motorhome. I was finding that the leisure battery was draining way too fast once the electrical hook up was removed.
This seemed very strange as all seemed normal. Both were giving a reading of about 12.6 volts which seemed fine but once disconnected from the charger would quickly lose power and be useless in a couple of days.
All became clear when I disconnected the batteries from the motorhome and measured them independently. One of the batteries was reading 6 volts. This is a dead battery and if yours is reading anywhere near 6 volts then get rid of it. The poor battery was pulling down the good battery and the good battery was making the poor battery look good.
Once the bad battery was removed, I did a recondition charge in the good battery and checked to make sure that it was still able to hold a meaningful charge.
I used a tester that puts a load on to the battery and lets you see if it is still functional. This is a very useful addition to your toolbox if you are having battery issues. Can save you a lot of time and expense if you can determine how good a battery is. A battery can read 12.8volts and still be a dead battery. The only way to determine is to put a load on it and see if it can actually power that load.
I have reduced the leisure battery to one battery and find that it works well. We have not had a problem since.
I actually have two leisure batteries but I don\’t have them connected in parallel, they are actually both independent and only use them one at a time. This is due to the charger, which is the original, not being powerful enough to charge both the batteries together.
I will explain this in another post if anyone is interested – Motorhome Batteries Explained.
The battery side of a leisure vehicle is quite complex there has been so much written about batteries and how to care for them and it can all seem a bit overwhelming. If you have had any experiences that may help others please leave a comment.
May 30, 2019 @ 15:31
H I do not agree with “Once they reach the 12volt mark they are flat and you should not use it anymore as damage will occur”
A fully charged 12 Volt Leisure battery, will very quickly fall to 12.5V or less in a hour or so of moderate use, at 10.5V it would be considered fully flat. All Leisure batteries like to be kept close to full charged, once charged their shelf life is very long when new. I would say you need to start thinking about recharging at 11.5V. A 200 Watt solar panel will allow you to wild camp all summer, providing you have an MPPT charger, or at least a PWM charger. A DC current clamp meter is the best way to find out where the power is draining away.
May 30, 2019 @ 21:24
A while back I would agree with your figures but generally 12 volts or under is regarded as flat. These figures are not from me but from battery manufacturers, some retailers have the same information.
You can run a battery much lower but there will be damage to the plates and will be very difficult for the battery to recover shortening the life of the battery.
Of course the most manufacturers recommend a 50% depth of discharge (DoD) which is actually around 12.4 volts. Just remember these voltages are measured when the battery has no load.
So when the battery is connected to the motorhome or campervan you sort of have to guess as the voltage will be lower under load which makes battery management even more of a challenge.
I have tried to explain batteries a bit more in this blog post;
Here is some info from Yuasa Batteries
May 30, 2019 @ 22:46
Hmm ???? it sounds like to me the manufactures do not want to admit the fact the full deep cycle batteries only have 50 to100 cycles. So at 30% discharge they want you to recharge so to extend the life.
They should then reduce the advitised AMP Hour capacity as 32Ah not 110AH.
My background is submarine lead acid cells we only came up to recharge when we had to
May 30, 2019 @ 23:24
I think you have hit the nail on the head. The sweet spot for wet batteries seems to be about the 30% mark to get the number of cycles advertised.
The only batteries that seem to get round this are the lithiums which can be discharged 80% for thousands of cycles. They are about a grand to buy so you have to use your batteries seriously to get your moneys worth.
November 23, 2019 @ 08:35
Are my leisure batteries(2) dead /need replacing. It’s winter .. I have no electric hook up. But 2solar panels. I am stationary waiting for other work to be done on my Motorhome and in the wait..I am living on board Last night I charged the battery by running the engine .. after about 15mins it reached 12.8 on my interior digital readout..after switching everything I could off ie heating, lights, at 2.30am I still had 12.2 in the readout.. but by 6.45am it was down to 10.8
I have charged it again by running the engine and am back to 12.7
I will be able to get EHU tonight..
How do I know if I should replace them or not?
Thank you in advance
May 18, 2022 @ 08:59
Hi Carol, did you get it dorted. I have a similar problem. I had the battery load tested and showed as OK, but still doesn’t hold yhe charge. On board display shows between 0 and 0.2 amps being drawn so should be fine.
June 15, 2020 @ 11:23
I’ve recently installed a new battery and VSR to my camper and have noticed it hasn’t been charging. In fact on some drives the leisure battery power seems to drop significantly. Could it be that the starter battery is drawing power from the leisure battery? I thought power could only flow the other way through the split chargers? And if I’m right could it be a faulty split charger do you think? My starter battery did recently go flat so I recharged it with a battery charger. So the leisure battery is in a better state than the starter battery. But as I said I thought that power could only be drawn into the leisure battery not the other way around.
Any help would be greatly appreciated.
June 26, 2020 @ 10:12
You might have a faulty split charger. The first place to check is the actual batteries. I would fully charge the batteries. Test the batteries with a battery tester which puts then under load (they are about £30) to make sure they are in good shape. Disconnect each of the batteries in turn and see if there is any power drain. So, just have the leisure battery connected but not the starter battery, leave for a few days and vice versa. Test the voltage at each stage of both batteries.
This will let you see if the batteries are holding a charge and if there is something pulling down the power.
You may want to check that your leisure battery is actually getting a charge when the engine is running, the voltage should be over 14V when the alternator is charging.
I had a really poor battery in our motorhome. It took a while to find the problem but the faulty battery was pulling the power from the good ones. All was well with the multimeter and each battery looked fully charged. When a load was put on the battery it was a different story – the duff battery would just die but would show a healthy voltage of about 13.4V.
It can be time-consuming finding faults in the van. One of the things that killed one of our batteries was the inverter, if you have one make sure it’s off.
Hope this helps a bit
September 23, 2022 @ 16:22
Our engine battery and leisure battery have both died , we are just back from a week away 3 nights on electric hook up then drove about 30 miles home o n Sunday 18th , tried to turn it on yesterday ,
June 27, 2020 @ 17:01
Paul’s advice is sound, I cannot fault it. if you have a clamp meter, and you join two batteries together that are fully charged there should be no or little equalising current, this was not the case with Apollo 13, they had shut down all power, as their fuel cells in the command module utility’s module had loss all its oxygen; The crew need 20 Amps max to bring up the guidance computer, but the batteries in the command module could not supply this for the time required, the answer, was to connect the LEM batteries in parallel before they discarded it, this gave them enough power to bring up the computer before they let it go! So you are not alone with battery issues!!
June 29, 2020 @ 21:57
Your van sounds exciting Andrew, look after those LEM batteries!
(Loved that film, by the way)
October 22, 2020 @ 05:37
To be honest your article is informative . I search many site to know about The main causes of battery drain is a faulty leisure battery. but I didn’t get the information I needed.
I saw your site and I read it. I got some new information from here. It is beneficial for many more like me.
Thanks for share your kind information.
October 23, 2020 @ 17:39
Hi guys, can I have my motor home completely rewired with a whole new system – charger, control panel etc….. .? Thanks in advance pete
January 26, 2021 @ 08:53
It’s certainly possible, I would imagine it would be a pretty big job with a cost to match.
November 9, 2020 @ 16:36
Interesting and informative article, thanks. Can I ask a question?
If you had a new 115ah battery that you knew was working perfectly, but every time you switched on the habitation area 12v system the voltage dropped significantly, to the point where lights were dim and the water pump dropped the voltage dramatically when in use, where would you start troubleshooting?
I’m in Scotland as well 🙂
January 26, 2021 @ 08:57
I would start at the fuse box for the habitation side. Pull the fuses one at a time (power off, then power on once the fuse is pulled) and see if there is a particular circuit that’s causing the problem. Hopefully, there is and you can narrow down the search.
January 26, 2021 @ 11:33
Something is puling a lot of power, (assuming it is not your command module guidance computer that you will need for re-entry and considered essential !)
You could put an ammeter across the fuse terminals (fuse removed), however, if the current is over 10 or 20 Amps, this may well blow the internal fuse of your amp meter, so a word of caution.
Another way, as Paul, says is to remove all fuses and replace one at a time, measure the voltage on the incoming supply to the fuse, than fit the fuse and check the volt drop. For example lets say you have 12.7V coming in, and you fit the fuse and the voltage drops say to 11V, than you know you are pulling some high current, or your wiring is very thin! if is drops to 12.6 then that circuit is fine or not doing very much. lead acid batteries can deliver 1000’s of amps, so be careful.
I do recommend a Digital Volt meter with a current clamp. make sure it works on DC not all do, They are not expensive from the right supplier £25 or so. see https://www.amazon.co.uk/Meterk-Multimeter-Capacitance-Resistance-Temperature/dp/B072QYZ7LR/ref=sr_1_5?dchild=1&keywords=clamp+meter&qid=1611660603&sr=8-5 for example. The beauty of these meters is they do not disturb the wiring, just clamp around the wire feed your circuit.
March 23, 2022 @ 09:15
I have a 350w solar panel.
2 x 110 batteries my epever unit tells me 100% even if I use a little power like an led or anything else immediately it starts reading 56% how can it loose so much power so quickly
March 28, 2022 @ 18:43
Sounds like a cell problem in a battery. Need to test each battery individually and see if they can carry a load.
August 22, 2021 @ 08:47
Hi this is a great article thanks…
We live on a boat so similar, just larger set up with our leisure batteries. We had 5x110ah leisure batteries which has run everything in our boat seamlessly including a 24/7 240v system via 1500w inverter for our fridge. (lots of boaters now use this as fridges are so energy efficient these days the discrepancy in energy usage between that and 12v is minimal).
As i say this has been perfect for us until the past 5 months or so…our inverter started to beep at around 5am suggesting not enough energy to power it. This has been a saver for our batteries because it stops them being discharged too much. We disconnected everything and tested each battery in the morning, so not fully charged, and 1 was showing 10.8v while the other 4 were at 12.85v. we removed this battery from the circuit hoping it was the culprit…but the inverter still went off in the early hours.
We are stumped. We run nothing but the fridge overnight which up to now has never been a problem. we do have lights to the voltmeter on out switchboard so could it be something on here discharging them??
We haven’t tried testing the batteries under load. It’s a bit hard to disconnect batteries for a few days when we need them for our water pump, fridge etc.
I’d love to hear any ideas you have…
Abi & family
August 26, 2021 @ 20:59
Sounds like a great system you have set up.
I had a problem with one of our batteries. It would show a nice 12.8V, or thereabouts, but under load, the voltage would drop dramatically.
There is no easy way to detect this but I did use one of these – https://amzn.to/3yiVbpO – a Battery Load Tester
It puts a large load on the battery – looks like a heating element inside it. This will show up most problems with batteries.
Probably quite useful when you have as many batteries as you have.
Hope this helps.
August 27, 2021 @ 10:44
Hi Abi, are the five batteries in parallel? this makes 550Ah, !! there is no perfect set up, if one 12V battery is down, it will hog the charge from the good batteries. I presumed they are charged from the the alternator or solar panels or both?
check cells are fully covered and none are dry, assuming it is not sealed
Load test the low battery, see what happens, if any cell bubbles than it has gone to the big battery in the sky!
If it is just flat (unlikely, as all would be flat), and no cells will bubble, try recharging it on its own, if it does not get up to 13.8 -14.2 on charge after a few hours at the 20 A charge rate, it is toast, check cells are fully covered and none are dry, a duff cell may bubble. When fully charged and the charger is a constant voltage 13.8V the cells should spit slightly. What is the age?
leisure batteries that are fully charged and only drained to 80% then recharged should do some 1000-1500 cycles, to get a battery to 100% you need an intelligent charger MTTP type. Hoe this helps
BR Andrew (ex submarine engineer)
March 22, 2022 @ 14:06
What a helpful page, thank you! I measured the current flowing from my leisure battery to the campervan and found a constant flow of 0.66 amps. Most of it goes to a circuit that I think has just a stereo on standby and a usb charger that is switched off.
Am I right to think that is far too high?
(By my reckoning that level of drain gives me about three days of camping (without even using any reading lights) before the 105ah battery needs recharging.)
I appreciate you answering folks’s questions. Joe
March 28, 2022 @ 18:46
That does seem to be a bit much. Try disconnecting the stereo and see if you can isolate the power drain. If it’s not the stereo you will have to try and find what’s drawing the power.
We had an inverter in the motorhome that would draw about the same power as you are seeing while just sitting – could it be an inverter?
April 1, 2022 @ 15:13
Hi we have just got out first camper a Renault master timberland endevour. battery seams to have died. Message in display reads engine started system disabled. We have solar pannel which said fully charged. Has anyone had this problem.?
June 6, 2022 @ 12:01
Hi guys i have a problem with my Leisure batterys run down whilst mobile in my motorhome,I have done all the standard tests but i am confused what the cause may be, I can charge up my batterys to maximum through the mains sytem no problem drive for say 3 hours park up i may be lucky to have 2 hours power for the tv ect pretty poor, charge up my batterys ,remove the fuse to my altenator from my leisure batterys on board system whilst driving ,job done 12 hours and more of power all batterys in good condition also the invertor is new,nothing left on to draw power just confusing. thank guys George.