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Battery gremlins

pauljmcnulty

pauljmcnulty

Active member
Ok, you may remember I had a battery die literally overnight a couple of months ago. Two years of no problems at all, then a drained battery that held no charge after 36 hours on a charger.

I replaced it with a Halfords battery, and it worked absolutely perfectly for about 8 weeks. Yesterday, battery is absolutely drained again. [&o]

Assuming that this could be two dodgy batteries and a huge coincidence, what else would cause the car to work so well for so long, then overnight throw a wobbly?
 
What that soulds like to me is not a battery fault but an intermittent or developing minor electrical fault. As if some circuit or other thing is staying energised, draining the battery, but not always.Something like a sticking bonnet-open switch on the under-bonnet light circuit.
 
2 options seem equally possible. I suppose if it was a very intermittent drain - once every 2 years could take alot of finding - then a good 2 year old battery should recharge ok.
Equally if it won't hold charge then it must be the battery - hopefully it is still under guarantee.
 
AS said - test the battery to see whether it is faulty; will it hold a charge if left on a slow charger overnight?

It could be an intermittent electrical fault, which would be a pain to chase. (Not difficult, just time consuming.)

Why not take the battery back to Halfords and get another one (they may test the old one for you which would answer your question), and see what happens with the new one. If, one morning, you find another dead battery, hook up some jump leads to the battery from another car, but don't try to start it; use an ammeter to measure the current flow from the battery to the car (you'll need to pull one terminal off to do this) and see if it more than a few milliamps. If it is, you'll be well on the way to diagnosing the problem.


Oli.
 
I'm taking it in to a local garage to get checked out on Tuesday, I can't spare the time getting it miles to the usual specialist as it's only an electrical issue. Any pointers about where to check first?

First battery died completely, wouldn't hold any charge at all. New battery was fine for a month or so, then overnight it's almost drained; enough to operate the central locking and boot, but not turn over. Two days and it's completely flat. Charging overnight and it's starting fine. Probably not alarm-related, as the system is fairly new and not arming it makes no differnece.
 
Problem solved. Touch wood......

Forgive me if I get the figures wrong. There was a constant drain of just over 0.3 on the meter, with the estimate for necessary drain down to things like clock, radio memory, alarm etc. a tenth of that. The mechanic went through a list of what would drain that amount, second on the list was glovebox light staying on. As I was in the passenger seat at the time I looked, and could see the light on through the gap. Pushed the lid properly closed and the reading dropped back to normal.

Job done, other than fixing it at some point. The reason for it being intermittent is that the lid usually pushes the switch, just that sometimes, I guess after a pothole or something, it doesn't. The difference is absolutely minute.

£24 plus VAT, the second cheapest fix for a broken-down 944 after a new DME relay. [:)]
 
paul, do you keep the glovebox locked?

on mine, if its not all the way home and the knob isn't turned to secure it, it pops open on really bumpy surfaces. i keep it locked and it stays put.
 
Paul, do you happen to remember what else was on that list of things which might draw a similar current?

I have a similarly temperamental battery and have never managed to get to the bottom of it. Sometimes I can leave the car for three weeks and find it still well charged, other times it runs down over a couple of nights in the garage.
 
ORIGINAL: poprock

Paul, do you happen to remember what else was on that list of things which might draw a similar current?

I have a similarly temperamental battery and have never managed to get to the bottom of it. Sometimes I can leave the car for three weeks and find it still well charged, other times it runs down over a couple of nights in the garage.
Click to expand...

The original suggestion was that any electrical part between the front bumper and the back bumper could be at fault. It was very obvious with the meter on to see the reading drop stright to standard when I pulled the fuse, or pushed the glovebox lid to switch the light off. The way he was going to tackle it was to pull each fuse in turn to at least narrow it down.

The drain from the things that stay on (clock, alarm etc.) is very small on mine, so it should easily last for weeks without an issue. The increased drain was exactly what he would expect from a single bulb permanently on, so the interior light, boot light, under-bonnet light or glovebox were the first place to look. He did say that pop-up lights often cause a problem where the movement chafes wires (something that used to crop up almost daily on Titanic years ago, are they all fixed now? [8|]). The most common problem, as we all know, is aftermarket stereos and alarms. According to the paperwork mine had several alarms removed, the wiring restored to standard, then a modern system fitted, so that didn't seem likely to be the cause of my problem. I'm just glad it was a simple fix, although I haven't tried to start it today. [&:]
 

ORIGINAL: pauljmcnulty
The way he was going to tackle it was to pull each fuse in turn to at least narrow it down.
Click to expand...
A very simple, very useful, fault diagnosis trick. Well worth remembering. Slight snag is that you need to connect an ammeter in series with the main battery connections, which is a smidge fiddly, but once you have worked out how to do that (easy if you have two people) then it is pretty simple to find a current drain problem.

One worth remembering.


Oli.
 
I can see I'm going to need to invest in a meter at some point. Thanks guys, that is a helpful wee guide.
 
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