www.jec.org.uk

Hi, I bought my first XJS 3 months ago, a 1994 4.0 Convertible. Since then I have been having battery problems. it is a new battery, and the garage have checked out the alternator, but the problem is after a couple of weeks of non-use the battery is dead. Now it is so dead I am having problems recharging it. Can anyone tell me if it is normal please for batteries to drain this quickly, and what do you do to keep it charged up?

Thanks
Mike

When they check the alternator they should maybe had check the battery drain as well with key removed. THats done be disconnecting one side of the battery and inserting an amp meter in series. Mine shows 50mA or so. Don't forget that the boot light switch will need to be pressed or that will muck up the reading. If you haven't a meter to use you can get away with a 4W light bulb instead between the battery post and disconnected clamp, that should not light.

Quite often this problem can be traced back to the boot-light switch. Worth a check.

Nick

If I'm not using the xj-s for a week or more I connect an Optimate battery conditionerhttp://www.optimate.co.uk/
Note, this won't charge a flat battery but will keep a good battery in perfect condition allowing for normal current drain.
There could be a reason for abnormal drain of course, which needs to be cured first Unfortunately once a lead-acid battery has been completely drained of power there is a chance that it will never recover.
Pop

Thanks everyone for the advice. I've had the electrics tested, got a new battery, got a battery conditioner, so we'll wait and see if that does the job!

Hi folks,

I'm suffering from these battery problems too. My car has destroyed a couple of batteries in the last few years, and the current one is looking like it's on its last legs too. So I conclude it must be the car, and not just a run of bad luck in battery purchasing.

For my current battery (no pun !) I am at the stage where I just connect it up when I want to use the car. All I had to do last time was to put it on charge for a short time, to kick it into life.

I suppose at some stage I'll have to ask an expert to track down which faulty component is causing the power drain. I have my suspicion that it might have been the siezed central locking motor in the passenger door (now disconnected). Another suspect component I remember reading about was when water got into someone's electric aeriel motor unit and the water was not draining out from it as it should.

Regards, Julian

If you can get hold of a multimeter, do what Mark B advised and pull fuses one at a time until you find the problem. Many years ago I had the same problem and found it was the heated rear screen/heated rear view mirror circuit. Never replaced the fuse as I don't need the defrost facility, never had a problem since
Whilst on the subject of battery replacement as others will be reading this thread, Halfords sell one, HB075 that was a perfect fit for mine with the correct vent nipple. I *think* the V12 uses the same one, but best check before buying.
Pop

I had a similar problem, turned out to the the Alarm on the car.

Hi guys,

A couple more possible culprits there then:

1) Car alarm - I've always had my suspicions about that too

2) Heated Rear Window - I had a new one fitted a few years ago, but it doesn't seem to work now

Thanks for the input

Julian

http://cpc.farnell.com/productimages/cp ... 981844.jpg

AT-838
UNBRANDED
CPC SOLAR - BATTERY CHARGER 12V
www.cpc.co.uk
product code CP02939
£10.95
(£12.87)



Another update: A colleague demonstrated to me a solar panel the size of a postage stamp which produced more current!

JUST AN UPDATE ON THIS, I'VE HAD 2 OF THESE SOLAR TRICKLE CHARGERS AND NEITHER WORKED!

THE COMPANY SELLING THESE TESTED A PILE OF THEM IN NEW STOCK AND NONE OF THOSE WORKED EITHER AND WERE SUPRISED HOW LOW THE OUTPUT WAS... THEN THE NEXT DAY THEY'D CHANGED THEIR MIND AND SAID THEY 'PUT OUT A SPECIAL KIND OF SOLAR-PANEL CURRENT' THAT IS NOT DETECTABLE WITH A DIGITAL TEST-METER!

IN BRIGHT SUNSHINE UNDER THE WINDSCREEN, BOTH MINE ONLY PUT OUT A SINGLE-FIGURE mA OUTPUT, WHICH WAS MUCH LOWER THAN THE 50mA STANDBY DRAIN FROM BATTERY!


-- MARK

mmm now that's given me a lot to think about.

My battery has run flat in the past few weeks because the boot wasn't shut properly (the misses). My central locking has stopped working and sounds like a sticking solenoid as my battery is also running flat again. Guess I can hold off replacing the battery until I have eliminated the solenoid problem. Solar powered battery charger seems a great idea - does anyone know if it works?

Solar powered battery charger seems a great idea - does anyone know if it works?
Not if your car is parked in a dark garage like mine
Pop

I had similar problems. One was boot light switch not being closed when boot lid closes. I taped some 2p peices to the boot lid to act as a shim. The next battery drain was caused by the electric antenna motor always trying to open / close a stuck-at-half-open antenna.

I recorded that the boot lid lights would draw about 0.7 amps from the battery and the antenna motor draws about 2 amps. I used a digital multimeter with the current setting and the meter in series between the battery 12V and the main 12v cable.

Sinclair

About battery drain... If you have a "60 amp/hr" battery, after a while it's usable fully-charged capacity becomes much lower than that, and yet can still start the car with just 1A/hr of capacity left!

Now, if the standby drain is 0.05A, that works out as 1.2A/hrs per day. Over a week that's 8.4 A/hrs.

Now you know why 70s/80s Jaguar batteries go flat!!


P.S. See my update on solar charger above /\ /\ /\

Here's a bit of myth-busting wisdom I'd like to share, to get this information I destroyed 2 brand new batteries - in the name of science

About battery drain... I did an experiment with car battery capacity some years ago. If you start out with a brand new battery with say, "60 amp/hr" printed on it, after only a few partial discharge/charge cycles that 60 A/hr charge capacity rapidly reduces at first, levels out and eventually stabilises at a rather low value very much less than 60.

All the time this is happening, the voltage remains the same and you would never notice this, but get this... a car battery can STILL start the car when there is just 1A/hr remaining of the orginal 60 A/hr of capacity left! A car start will require at the very most 3 seconds of 500 Amps, which works out as a fraction of an Amp-hour of energy. Because of the internal geometry of a car battery it still delivers a big current while the last dregs of energy remain.

When there is no standby current drain in a car, the battery has an easy life and with the majority of cars becoming like this, the battery naturally evolves into the cheapest way of providing the bolt of energy, at the expense of other qualities such as tolerance to deeper discharge cycles (which would never be used).

Now for some more sums, if the standby drain is 0.05A, that works out as 1.2A/hrs drain per day. Over a week that's a now a total of 8.4 A/hrs of discharge. This is not good for a car battery with low tolerance to deep discharge, as it's design has probably been optimised to be cheap to make instead.

This is why disconnecting the battery makes the difference between starting or not starting after a period of non-use. If your battery has degraded to 6A/hr and you didn't disconnect it, then after a week it would be too flat to start the car.

This is also why the battery conditioner works so well, and why it's also (in part) a myth that the charger main function is to 'keep the battery topped up with charge'. This is because at the point of connecting the charger, the battery is already fully charged from the journey home (if the charging system is working correctly) and a battery's self discharge is very low in comparison with the standby current drain. The charger is actually supplying that 0.05 Amp standby drain (the charger believes the battery is taking the current, but it doesn't matter). Since the charger is providing the standby current instead of the battery, the battery lasts a lot longer.

So the conclusion is, the best thing you can do is attach a charger on the same day you leave the car for an extended period. The charger doesn't need to go directly across the battery if it's only ever supplying the standby current, it could connect to say the cigarette lighter for example. The charger must be the kind that can be left on permanantly without damaging the battery. If you don't have a charger and know the car will be idle on a regular basis for weeks at a time, it will be a good thing to disconnect the battery. However, remember it might be better for you to 'spend' a battery if you require the car alarm to be active or don't have the radio code to re-enter.