I’ve read as many posts as I can find on the forum which sound like they might relate to my problem but haven’t found a solution so hoped someone might be able to point me in the right direction.

On my 2004 2.0 diesel x-type the battery light is permanently on and the battery fully drains itself every few weeks. So far I have had a new alternator and new battery put on my car by the garage, both of which have done nothing to sort the problem, so I’m trying to figure out what might be causing it before throwing any more money at it.

I’ve read a number of similar posts by thermo on here suggesting that the battery cables could be faulty, so I performed a voltage drop test from the main stud on the alternator to the positive cable of the battery, which only came up with a drop of max .38 volt, which sounds normal? I also tested from the negative cable to earth and this drop was even lower.

Across the battery terminals whilst the engine is running I am seeing a voltage of around 14.2ish volts and doesn’t drop to below 14v under load with lights, blower,radio all on, which leads me to think that the regulator is allowing the new alternator to put out the correct amount of current to charge the battery.

I’ve run out of possibilities I can think to test for, has anyone got any suggestions? Thanks in advance!

 

You done all the logical steps to sort it out that I know of..With an alternator output as good as you claim, it isn't the cables or the alternator. ONLY THING LEFT IS ONE OF TWO THINGS..1) A parasitic drain from something being on (set your DVOM to DC AMPS and put it in series with the Neg lead [between battery neg post and lead to ground] and see if there is a large current draw (amps), or 2) Your new battery is crap to begin with and that is not unheard of.

 

Thanks for the reassurance, at least I'm not missing something obvious, any ideas whether a parasitic drain would trip the battery warning light? I would have thought that might happen when the engine is off and there is no charge being transferred to the battery, but surely it would go away once it's fired up and there is voltage being supplied by the alternator to cancel out the effect of a short/drain somewhere else?

I'll go and test for amperage draw now anyway, what might be a considered a large current draw with the ignition completely off?

 

An AMP or more is large enough to pull the battery down while engine is off..Double check the battery terminal voltage when at idle too..just to be sure it isn't the cables..Mine would show around 12-13 volts after a few minute of running..14 volts right after start up, then fall down enough to trigger the battery light.

 

Currently (HA!-sorry) I'm getting 0.1A draw whilst the car is off, I'll double check the voltage between the terminals again after I've taken it for a run this afternoon

 

1/10th amp is about normal..

You don't even have to drive it..Just start then note the voltages and wait at idle about 10 mins and check again.

From what I learned on mine..The system charges at a higher voltage right after start up to replenish the battery from starting, then kicks down a couple of volts for float charging..It still should still be over 13 volts at the lower charge level.