I have a problem with my battery draining rapidly on my 1999 Jaguar XJ8. The battery test good as well as the alternator. I took the car to one of those auto part stores and they ran diagnostics on the car. While the engine is running, the current draw on the battery is greater than the alternator can generate. Any idea where I should start checking? Is there a common grounding problem with the car?
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I have less than fond memories of tracing electrical troubles in a Jaguar (though much older than yours). Here's the basic process you need to follow:
1. Pull all the fuses. Does the battery drain overnight?
If yes, then a circuit that is not fuse protected is the problem. Start with starter/solenoid, etc. Disconnect each thing and test with meter.
2. If battery drain stops, then use meter to check current drain on each fuse. One will have more than a trickle.
3. Once you find which system is draining, you can narrow it down further by disconnecting each thing on that circuit.
Yeah, It's a pain, and may take days, but you can find it.
You have a current leakage between the positive terminal and the earth. Place a ampmeter in the circuit (remove a bat terminal ans connect in the meter) and read any current flow. Have your battery tested at a battery shop as they fail internally and short out in the plates
You may have a parasitic drain on the battery.
Check the voltage on your fuses after you turn it off. Wait 5 minutes before doing so.
Hook up an Amp meter in series with the battery and see what the current draw is. If it is more than 250 milliamps you have a parasitic drain.
ok, just because the battery is cranking over, does not mean that the cell inside the battery are not weak. they will always take a charge. but as to how long they will keep that charge is the problem. all 12v systems are as follows so check yours.
all should have no more than 14.5v during a charge(engine running) anymore it will fry not only the battery, but other componets as well.
all should have no less than 12v with the engine off, and a load test of no more than 15sec, and a drop of 10v or higher should be present.
with a good battery and alt, there should be a drop in voltage no less than 8v during a start crank, and after it starts it should rapidly return to a 12.5v to 14.5v charge. I suggest to have the battery and altinator tested for a load, and cell state.
If battery is good and has past a load test, then with car running put a volt meter on the battery terminals, 1 on positive and 1 on negative, they should show approx. 14.5 volts. dc if alternator bad it will just show battery voltage or 12 volts dc.