Like others have posted, my 84’ has a slow drain on it somewhere and there’s a pretty hard start after a week of not driving (seems to have gotten worse as outside temps have dipped into the 40sF). In the meantime, I’m thinking of taking the battery out while in storage this winter. Is there any reason this wouldn’t be advisable? And, is there any trick to removing the battery? Ok to simply disconnect the cables and leave the battery in place?
Thank you for your help.
I disconnect my battery for long term storage, I do remove it from the trunk and put it indoors since it gets fairly cold over the winter and I fear it freezing. I can think of no serious harm caused by disconnecting the battery. Other than resetting the trip computer things should be back to normal once the battery is hooked up again
I would leave the battery in place, but disconnect the negative lead. That’s all. Then I would leave a battery tender on it. I have two Noco ones. Work great.
The battery still has self discharge when disconnected, and s tender is essential for its health.
Yeah a battery tender or a charger with a trickle charge, maintain function is ideal. As for leave it in the trunk charging, I personally would want that indoors, if you park outdoor I would be weary of leaving a charger connected
Interesting topic.
What is your take on connecting the battery tender without disconnecting the battery from the car?
Thanks for the replies. I have tried a trickle charge for a week once, and the car was still a very hard start. And if I do that, the trunk has to stay open for access and I’ve been wondering if the light (bulb is removed) is somehow the culprit for the drain.
Car will be parked in an unheated garage.
My self car mechanic skills are limited to disconnecting, removing, and trickle charge. So, suggestions for best course of action?
What do you mean by trickle charger? The older dumb ones are pretty useless, managing to combine very slow charging with ultimate over charging.
You need a modern multi stage one like the Noco Genius. My larger one charges at 3A, then switches to maintenance mode, but will switch back to higher rate if needed.
I already answered your question once. Disconnect the negative lead, and connect a proper smart battery tender. Leave the trunk ajar for ventilation.
I am a little concerned that you have misdiagnosed the problem - assuming that the car is hard to start after a week, therefore I have a drain. The alternative is an old, sulphated battery with minimal storage and high self discharge that thus has marginal ability to start the car after a while.
You need to determine if you have a drain, or a weak battery, or both.
No problem, unless the car has a serious power drain when off.
I got fed up with disconnecting the battery when I had to work on the electrical system, so I installed a knife switch.The battery is an Optima, with a maintainer permanently attached.
Connect the leads from the trickle charger to a cigarette lighter plug. Lower
one window on the car, run an extension cord in through the window, plug
the trickle charger into the cigar lighter, and set the trickle charger on the
console. Unplug and set aside when driving the car.
– Kirbert
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Thanks everyone. @Mark_SF the trickle I used was ~20 yrs old, 1.1 amp I think. I’ll pick up that Noco, 3A at your recommendation. Thanks.
Regarding the drain, the battery is new as of this summer. After initial install, it was a hard start one week later.
Here’s what you can do. After one week, disconnect the battery and measure the voltage with a reasonably accurate meter. The voltage will indicate the state of charge. It’s a linear scale from 12.6V fully charged, to 11.9V fully discharged.
Then re-connect it, and measure the battery voltage at the terminals while cranking. Will probably require an assistant. I would expect at least 9V, preferably 10.5V.
Report back here on the results.
Another thing to check is whether there is indeed a parasitic discharge. If you have a multimeter remove the neg lead and insert the DMM (digital multi meter)
In series, wait for the computer to go into sleep mode and then start pulling fuses to see if the resting amp draw reduces on one of the circuits. I don’t know what the draw should be on the XJS but somebody on here will have that answer.
If you charge the battery while it is connected to the car, and the car has a current leak, then you are just feeding the leak. Find the leak by narrowing the possibilities through pulling circuit breakers.
Doesn’t always work. I had a really hard one on an XJS some years back, where a bracket guiding 2 wires back up between the transmission tunnel and the transmission was left dangling during a long-ago warranty transmission changeout, Eventually the vibrating bracket ate through its own insulation and the insulation on both wires, shorting the 2 wires together intermittently. Circuit breaker pulls did not diagnose it, it only mattered where the bracket settled when the vehicle was parked. Sometimes the battery would discharge overnight, but usually not. Aggravating! I could not count on the car to start in the morning, could not find the problem, and electrical shops failed to find/fix the problem (although they all had some item they “fixed” to justify their bills), I was just throwing my money away. I resorted to a “green knob” switch and used it religiously whenever I parked the car. The errant wires could not be seen even from beneath the car on a lift, and the car suffered intermittent battery discharge for years before a mechanic doing a starter changeout happened to discover it (one of the wires was connected to the starter solenoid).
I have one car (1993 Camry) that is stored in an unheated steel storage building every winter. I use a “green knob” switch on the negative terminal to disconnect the battery while its in storage, and it starts up fine every spring for perhaps 5 years before the battery finally expires.
If you have an Optima battery (2 of my cars have them) that is discharged, then charging may need to be done with a second (lead-acid) battery in parallel using battery jumper cables to connect them (positive to positive, negative to negative).
Having gone through some battery issues recently, I recommend this charger I borrowed from a neighbor (then bought one of my own):
https://www.pepboys.com/product/details/63791/01401?quantity=1 (available elsewhere, too)
It will automatically set the appropriate charging levels, including trickle charge, let you know where it is in the charging cycle, and also measure output voltage as per Mark’s suggestion.
My understanding is that measured draws in the 20 to 30 milliamp range are normal, but draws in the 200+ milliamp range are suspect.
Measure at the battery posts (all lights such as courtesy and underhood lights off), pull circuit breakers/fuses one by one until the draw drops significantly, and that circuit is the likely culprit. Now you have to find out what is on that circuit and then replace the fuse and disconnect each of those devices until the drain drops. Not easy if you have to drill down to those attached devices, but you may get lucky. Not always successful, since not all circuits/devices are protected by circuit breakers.
that in itself would make me suspect the battery! disconnect and see if it still drains overnight. I just chased a battery drain yesterday on the work truck. connect ammeter between battery and terminal (in series) and see if there is any current draw. if there is, remove and replace 1 fuse at I time until the current draw changes. that is the easiest way to check ‘most’ of the circuits. if all of the fused circuits are fine, then you need to check wiring before the fuse! in my case, it was a relay/solenoid but could be any wire, switch or part before the fuse, including the fusebox itself.
OK everyone - thanks a lot for the comments / advice. I’ve got my work cut out for me, will probably have to begin tackling in earnest in spring, for lack of time. For now, I’ll put the battery on a good recommended trickle. Thank you.
I leave my trunk open a lot… so, I have a flat metal tab that hooks to one of the trunk light switch screws.about 1"long and 1/2" wide…It is rigid and not overly thick…I push the switch button down and slide the metal tab over the button…the one screw is just tight enough to allow that manouver…no battery run down for leaving the trunk (boot) lid loose or up…easy to move back but I never bother …don’t need the trunk light really…
My 94 XJS V12 has a power drain on the battery that I have never been able to locate, so I installed a battery shut off switch to the battery. This has worked out great for me since I only drive the car every weekend or two. I used to have to charge the battery quite often since I don’t drive it enough to keep it properly charged. It only takes a minute to pop the trunk and turn off the battery switch. (No more dead battery worries)
