Jaguar XJ8 3.2L year 2000 - Battery drain

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Tue 17 Sep 2013 20:35
Jaguar XJ8 3.2L year 2000 - Battery drain - le1ont
The battery on my year 2000 XJ8 3.2L runs down to 20% of capacity and c.11.9 volts if left standing for two weeks after a run or charge, and the car on occasion has not started due to a low battery. Disconnected from the car the 100 AH battery, Bosch 12 months old, holds its charge and tests OK. An auto electrician found a current drain of only 0.2amps with the car locked, presumably for the alarm system. At 2000 rpm the alternator under load gives 118 amps at 14.1 volts. I now connect a mains battery charger for a few hours every week.
All the lights appear to switch off. The problem lies with the car, not the battery. Can anyone please suggest what the problem might be?
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Tue 17 Sep 2013 21:52
Jaguar XJ8 3.2L year 2000 - Battery drain - Galaxy

I would say that the current drain of 0.2 amps is high, and I'm sure this is where your problem lies.

A friend of mine has a Jagauar XJ12 fitted with the same battery as yours. He keeps the battery on permanent trickle charge with the car in his garage. He has told me that he doesn't lock the car because this causes the alarm to be set and the high current drain is encountered. (only unlocked when it's in his garage!)

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Tue 17 Sep 2013 23:44
Jaguar XJ8 3.2L year 2000 - Battery drain - elekie&a/c doctor

As a basic rule,to calculate the target drain on the battery,multiply the battery capacity by 0.6.So your 100ah battery will give 60 mA.The reading you have is 200mA.Much too high.This could be caused by anything electronic not shutting down fully.Even the radio could be a problem,even though it is switched off.The only way to isolate the fault is to disconnect fuses to numerous circuits and check the drain.If the car is kept outside,then it is possible to use a solar trickle charger.hth

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Wed 18 Sep 2013 00:12
Jaguar XJ8 3.2L year 2000 - Battery drain - Peter.N.

A drain of 0.2 amps will loose you approximately 1 ah every 5 hours so to flatten your 100 ah battery will take about 500 hours, if it flattening quicker than that I suspect you have lost battery capacity. The way modern batteries are constructed means that they will still provide enough power to start the car even when the are down to 20% or so of new capacity but they have very little in reserve.

My 406 Hdi battery goes flat if I leave the headlights on in less than 2 hours so it has a capacity of 20 ah or less and yet it starts the car instantly every morning.

I would agree that 200ma is somewhat excessive but shouldn't give a problem if the car was used regularly.

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Thu 19 Sep 2013 15:00
Jaguar XJ8 3.2L year 2000 - Battery drain - le1ont

Thank you all three for your comments. I have ordered a solar powered charger from Maplin giving an output of 0.4 amps maximum whch is double the measured drain, so will see how that works out before taking any other action. le1ont

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Thu 19 Sep 2013 20:35
Jaguar XJ8 3.2L year 2000 - Battery drain - Cyd

A quiescent current of 200mA is way too high. You should be getting closer to a tenth of this.

How did you measure it? Was it measured immediately after locking and with th ebonnet up?

You need to find the bonnet switch and hold it down or otherwise fool the car into believing the bonnet is shut.
If your car has double locking (aka deadlocking) then fully deadlock the car.
Watch the reading for at least half an hour to see if it reduces from its initial value. Many cars electronics don't go "to sleep" immediately upon locking, but wait for anything from 10 to 30 minutes, so they are "ready for action" if the owner has just stopped for a few moments.

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