Flat starter battery

Hi everyone,

Problem with my starter battery on Autosleeper Harmony 1998.

Battery flat recently so jump-started with our car and enjoyed a 2-3 hour drive and a nice day out. Started several times with no problem on return. The same happened a few days later and went through the same routine. Just happened a third time with the same routine.

Each time the van is left for 3-4 days the starter battery is flat again. After the second time, I removed the radio completely as it turned on every time as soon as we turned the ignition key and I thought this might be the cause but it's just happened again.

There is nothing in the cigarette lighter drawing a charge and no interior lights or number plate lights are on. The leisure battery is fine. All cabin lights working fine. I do not have a solar panel. Both the Starter battery and leisure battery were new five months ago when we bought the van.

It's not winter so I can't think why there is such a rapid drain on the battery! Does the leisure battery draw power from the starter battery when the van is parked? I thought they both charged only when the van was running.

Any help or idea's would be appreciated.

I guess an apposite first question in a case like this would be: were any changes made the vehicle, or was any work done on it, just before the problem started? If so, I would look at the areas worked on.

If not, the obvious first suspect would be a knackered battery, so it would be worth having that tested. Unfortunately it is possible for a new battery to be delivered in a faulty state (for example if dropped heavily in transit).

Then there is the question of whether the battery is actually flat, or only appears to be flat. There is one specific fault (an almost-failed connection from battery negative to the chassis) which can result in the engine jump-starting OK - because most people use the chassis instead of the engine negative terminal - but failing to start from its own battery, even though it can run Ok once started!

It is possible (but unusual) for the split charge relay to weld itself shut and cause the two batteries to be connected together permanently, but assuming the leisure battery is in good nick, all that would mean is that they will equalise - the starter battery cannot discharge itself into the leisure battery if the latter has no load on it.

If you have no other leads to work from, measuring the battery voltage accurately should give you further clues. It will tell you whether the battery is fully charged after the engine has been running for a while, and how quickly it is discharging. It sounds possible that the output from the alternator could be low, but you'll really only know that by measuring the voltage at the battery while the engine is running.

If the voltage measurements suggest that it is being successfully charged, you can then go on to measure the current drain while the van is sitting doing nothing. That can have complications on recent vans, but on a 1998 van it should be relatively simple, as you shouldn't need to worry about waiting for lots of control modules to go to sleep before you can get a meaningful reading.

A 2/3 hour drive will not fully recharge the battery, try putting a proper battery charger on and giving it a full charge up and take it from there, if it starts going flat again it possibly time for a new battery, or take of the battery fully charge and then have it load tested

If you have or can borrow a multimeter, set it up to read 10Amps, usually involves swapping lead around.
Set the rotary switch to 10A
Now, remove either battery terminal
Put one test lead (doesn't matter which) onto the removed battery lead the other on the battery terminal it was removed from
Reading should be zero with everything off. Now put ign/radio/more or less anything, side not head lights on and repeat.
Some current should now show on mutimeter, this is just to prove the multimeter is set right!.
Switch everything off again, meter should return to 0A.
This will prove whether you have a parasitic load somewhere, if in doubt try the meter on normal settings and mA, it could be a tiny load easily enough to flatten a battery over a few days.
Had a Triumph 2000 yonks ago, flat battery, bought new one, next morning,  new one flat. Put wifey in the boot, sure enough boot light was on!
BTW, if you want to see who is most pleased to see you, put wifey and dog in boot. leave for 1 Hour. Bet the dog will be pleased...............!!!!!!