Hi chaps. 2004 Jaguar XJ8. Something is drawing 4 amps at rest, so obvs battery is flat overnight. Got multimeter. Tried pulling a few fuses, alternator AC ripple test. Fault not found. Garages unenthusiastic. Last auto electrician ran away screaming. I use a Noco booster to start it. Workaround : disconnect battery overnight or when otherwise not in use. Battery in boot. Boot lock doesn’t work to pull boot completely shut if no battery power. Hmm. So if battery disconnected boot can’t be closed properly. OK - what about a remote battery isolator thingy. Problem seems to be that i’m told normal remote battery isolators can’t stand startup current. Is that true? So in the morning i ciuldnjust click the isolatir remote and start the engine? Hadn’t heard that before. If true i’d have to click isolator, open boot, disconnect isolator, reconnect battery as normal, then start car. Boot can be opened with key btw. Any ideas?
Car battery isolator vs CCA
- Thread starter elcaro
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Try them all, one must supply that phantom discharge. Also try disconnecting the alternator, that might be causing a discharge. 4amps 12v = 48watts, where ever that is going, will at least be warm.
I have 2 questions
1 how old is the battery?
2 have you watched RMS Diagnostics on you tube?
RMS is an auto electrician who describes his fault finding process. He is based in Kent, Sandwich I believe.
1 how old is the battery?
2 have you watched RMS Diagnostics on you tube?
RMS is an auto electrician who describes his fault finding process. He is based in Kent, Sandwich I believe.
Can't you push it down by hand?
This is a time for an IR camera.
Old salt, johnd, thanks. Battery pretty new, tested ok recently by RAC. No not seen that RMsYoutube. Boot lid can’t be pushed all the way down by hand, short of say just under a centimetre so maybe not quite watertight?
Yeah re warmth - is it possible to prioritise fuses to check? Some things must surely use less then 4 amps, so which ones do use that much I wonder
Yeah re warmth - is it possible to prioritise fuses to check? Some things must surely use less then 4 amps, so which ones do use that much I wonder
It could be more than one item, remaining on, so worth eliminating every one. Be aware - that your system will likely have a sleep mode.... After it has been on, if you turn it off, it may take a few minutes for it to go to 'sleep', where it minimises the current drawn. Disturb the electronics by pulling fuses, may wake it back up. Disconnecting and connecting an amp meter, in series with the battery, will also wake it up.
Mine, has an under bonnet fuse panel, which contains all the big current fuses, plus a few smaller ones. That then feeds a much larger bank of smaller fuses, tucked behind the glove box. It also has a handy bus-bar link, to isolate the battery, which the meter can be put across, without waking the system up.
A typical discharge, once into full sleep mode, should be between 10 and 40mA, versus the 4,000mA you are suggesting.
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Does the car have a scond battery for the security systems?
Ah yeah been disconnecting neg terminal then connecting a cable from battery negative to the negative cable, in parallel with the multimeter. Then wait 20 minutes. Then disconnect the cable leaving the multimeter connected. So all the current goes through the multimeter. Have to use this “shunt” method cos the multimeter times out
