Hi, Two weeks ago I bought a 1999 XJ8 4.0 with 85k on clock. She is a lovely car. However after being parked on my drive overnight the battery was flat. I recharged the battery and checked nothing was on but the same happened. I bought a new battery but 36 hours later the battery was flat. Has anyone had this problem before? many thanks for any help from a novice Jag owner.
Don't know that model but have had extensive experience with flat batteries on XJ6 models. First up, there is a lot of computerised etc. equipment in Jags, and unavoidably it takes a small drain. A good battery should be OK provided the car is used say once a week. Overnight flattening is much too fast and may indicate a very poor battery.
Next possibility, an aftermarket alarm. They often draw absurd amounts of juice when in the ambient condition. Check anything non-standard and added to the car.
Third possibility, boot (trunk?) light staying on, or some other light.
Scientific test. Place analogue (not digital) multimeter is series with battery lead (when battery is charged) to measure quiescent current. DO NOT ATTEMPT TO START CAR WHEN YOU DO THIS. Ambient current for the XJ6 was under
1 amp from memory. If much higher, something is wrong.The reason you need an analogue meter is that there will be a steady small variation owing to the clock pulses. On a digital meter that would make the digits constantly change. On an analogue meter the pointer just sways a little.
Hi Guys Just to let you know after visiting 3 Jag "experts" the prob was identified as a faulty air con sensor switch, which drained 5 amps per hours (always) compared to the ideal 0.5 amp an hour when activated. Cost £70 to identify and rectify so all well now. Many thanks to all who offered advice.
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