I have had the battery light come on at first it.

WAZZER18

MEMBER
2003 AUDI A6
170,000 MILES

I have had the battery light come on at first it just flickered but now its stayed on and the car died I managed to jump start it but as soon as I took the jump leads off the engine died again I replaced the battery and the car started fine but battery light still on I let it run for about 2 -3 minutes before switching it off and after about 10 minutes I return to the car and tried to start it again but this battery had also died. Can the alternator draing the battery whilst the vehicle isnt running? And can it draing it within ten minutes?

1 Reply

CARADIODOC

MECHANIC
33,871 POSTS

Wow. That's one heck of a sentence! With no punctuation I can read it at least three different ways, but as near as I can tell, the battery warning light is on and the starter won't crank the engine. You also seem to be confusing a lack of charging as something is draining the battery. To get you started in the right direction, the warning light was telling you the charging system wasn't recharging the battery while you were driving, and it started out as an intermittent problem. While there can be an intermittent electrical connection, most commonly that is caused by worn brushes inside the generator. As they continue to wear, the problem will occur more often and for longer periods of time. As you continue to run the engine, the battery is supplying the power to run the fuel pump and the numerous computers so it is going to run down very quickly.

There's two common issues with the jumper cables. First of all, while you might get enough of a charge into your battery to start the engine, those cables tend to develop poor connections and will stop supplying sufficient current until you wiggle them. Your engine will only run until the fuel pump or Engine Computer shut down. Second, when the battery gets depleted that far, it takes a good ten to fifteen minutes of charging with jumper cables, a battery charger, or a new generator before the acid in the battery becomes conductive and it STARTS to take a charge. Then it needs another hour or more at a slow charge rate to become fully-charged. Two minutes isn't nearly enough time for it to charge up so everything you're doing is with a dead battery.

Have a professional load test performed on the charging system. You can do a preliminary test with an inexpensive digital voltmeter. Measure the battery voltage with the engine off. If it's fully charged you'll find 12.6 volts. At 12.2 volts it's good but discharged. If you find closer to 11 volts, it has a dead cell and must be replaced. Measure the voltage again with the engine running. It must be between 13.75 and 14.75 volts. If it is low, suspect the generator.