Car Battery Going Completely Flat

martindow

Volvo 440 normally fine but occasionally after being left unused for 24 or 48 hours the battery is completely flat - even the clock is stopped. After being started from another battery it seems fine and starts easily until the next occasion the battery is totally flat. Nothing obvious is left turned on.

The battery was replaced a couple of months ago and according to the meter the breakdown man came with yesterday the alternator is charging OK.

Any ideas on how to approach this?

steveo3002

jump starting wont recharge the battery ...needs an overnight trickle charge , chargers are cheap enough at argos and the like

once its fully charged , you can set an ampmeter between the battery terminal and lead to test for something thats using power

likely culprits are alarms and stereos, and boot/glovebox lights staying on

steveo3002

http://www.clubgti.com/forum/showthread.php?t=170895&highlight=battery+drain

post number 3 describes the test but uses a bulb instead of a multimeter

goldspanners

check the boot light.
i remember a volvo 480 ( you know the wedge shaped one with pop up lights)
this was ridled with weird electrical faults.
the first one was the boot light was staying on all the time and draining the battery,all was well for a week or 2,then again more strange flat batteries,turned out the negative terminal from the battery had corroded where it bolts on to the bodywork,i think it was hidden under the battery tray.
best way to test with out taking out battery and tray is to stick a jump lead from the negative battery terminal onto a good earth point, strut top bolt or engine mounting bolt.

big_gay_kirk

Now this is a long shot.. but worth looking at.. had similar prob on a Volvo 240, and on an Allegro... at the back of the alternator (sometimes the starter motor) you will have a thin wire leading off a spade connector.. thsi is (apparently) a voltage regulator gizmo... strangley, there will be another post for a spade that is unused.. not sure why.. but if the spade is placed on the wrong post, your battry will drain in between 12 and 36 hours, depending on the battery... to fix, simply put the spade on the right post... not applicable to all cars, but it may be worth checking.....

tomstickland

Either the battery is knackered or some electrical item is draining it. Boot lights or alarm are common.

anewman

You can use something like this to test where current is being drawn You take the fuse out, insert it into that, then insert that and it will show you how much current is being drawn.

martindow

Thank you everyone. I have charged it up fully and am getting a current of 0.15 amps from the battery terminal to earth. I've checked there are no lights on in the boot and there is no alarm fitted. The only obvious thing drawing current is the clock. Or do radio CD players draw any current even when they are turned off? Is a reading of 0.15A OK?

anewman

15mA is nothing, and I would say that's ok. CD players *can* draw current if wired incorrectly.

What's the voltage reading now on the battery, now that it's been charged up and connected to the car for a while? It should be above 12.5v, Ideally between 12.6v and 12.8v I would say (assuming no electrics have been used). Just because the battery is new I wouldn't rule out the possibility the battery is faulty as I've made the mistake of assuming new bits aren't faulty before and looked at everything but what was causing the problem.

martindow

The battery shows 12.75V. The current is 150mA though (rather than 15) - would you still call that nothing?

anewman

Ooops, I got my maths a bit wrong :eek: 150mA could be a problem. Next step would be to do what you've just done and remove the fuses one by one to check which circuit the current drain is on.

I would say 12.75v indicates the battery is good.