Here is the problem-

1990 audi 200 turbo, high mileage

Engine will start, run for a little while, then low voltage and abs and brake lights come on and it will die. Voltage gradually falls to 8 volts before this happens.

Then, with the car off, voltage will slowly climb from 8 to 12 volts and the car will start again, but this takes a while. Putting the ignition key in the ignition or pushing the brake pedal, etc, causes voltage to drop during this recharging period.

Does this sound like an alternator failure? How is the battery recharging itself with the car off?

Battery is brand new, after replacing the original battery a few weeks ago, that thing was 15 years old an still working!

Thanks for any help

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It doses sound like it's the alternator, when the car is running and you check the voltage at the battery it should be 14v-15v if it is below this it means that there isn't enough voltage to charge the battery, next is to check that the voltage coming directly out of the back of the alternator is the same low voltage if so a new alternator is required.

The battery isn't rechrging it's self with the alternator off it just hasn't got to expend any voltage so it shows a higher reading.

The best way to test a battery is to do a drop test as you won't have this machine you can use a multi-meter simply put the meter on the battery and then start the car the voltage should not drop below 9V while cranking if it dose then you need to charge it then carry out the test again to make sure that the problem has been corrected with a charge.