Battery dilemma

Hi all. I'm new to all this forum stuff, and don't know much about my 1995 850T5 auto estate either. I am being given the run around between the garage that fitted a new battery(3 Year warranty) 2 years ago who claim the battery is OK and the car isn't charging properly ie it must be the alternator at fault, and an independent Auto electrician who says there is nothing wrong with the alternator, it IS charging OK.
According to the little green light that is integral to the battery; when I switch on headlamps the charge gradually drops until the light shows as discharged. When headlamps are left off the battery recharges after a run and battery light shows as OK. The point is - is the battery really faulty? Is the alternator acting up, or is something else entirely to blame?

Any suggestions to help me decide what to do next would be most appreciated. BTW I'm a complete novice at car electrics.

[ShadeTek]

Whay to do is if you can get a voltmeter and measure the voltage of the battery when the engine is switched off. It should read 12Vdc. If you can read the voltage off the ciggy lighter that will allow you to start the car and rev the engine. Then start the engine, the voltage will now rise up to anyhthing between 12vdc and 14vdc. If you rev the engine you will see the meter readout go up. If it doesnt, your alternator is not charging the battery. If you don't have a voltmeter, leave the interior lights on in the car and see if they brighten when you rev the engine. Another good indicator the alternator is outputting a voltage higher than your battery.

On the other hand you may have a drain on your battery which is eating your power away overnight or when parked at work, I.E. the boot light or the rear festoon light on the estates is famous for that....or even the glove box lamp. Garages can test the capacity of your battery for you if you drive in and ask them. They basically short it out and measure the current the battery can supply.

Thanks for your thoughts. I actually saw the electricians meter reading 13+ volts with the engine running and the headlights on. Whatever it is, it seems to only drain the battery when the engine is running.

[Richardkimber]

Colin,

It might be that you have a high resistance in the earth strap or cable that goes from the engine block to the chassis/batt -ve terminal.
One way of testing this is to measure the voltage between the battery -ve terminal and the engine block with engine running and full electrical load on (heated screen, fan and h/lights on full). It should not be more that 1 - 1.5 volt. Try placing jump lead between the engine block and the battery negative terminal, if this substantially changes the measured voltage you have a high resistance.


Richard K

Richard,
Thanks for that. It sounds like a good contender. If this is the case does it mean that there is a poor earth connection, or do I need new straps? (I did say I'm not much on car electrics :-)

By the way, I've now installed a new battery, so we'll see how it goes.

Regards Colin.