XJS ( X27 ) 1975 - 1996 3.6 4.0 5.3 6.0

Battery drain - No cranking, revisited

Old 05-29-2019, 08:52 PM
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Default Battery drain - No cranking, revisited

Not just XJS or Jaguar related, but good info should a member experience this rather odd electrical problem.

I have previously posted regarding a battery drain on my ’94 XJS and then about a starting issue (wouldn’t crank) that dragged on forever, causing a series of hard to figure events.

The car sometimes started with the battery just charged, but if I waited one more day it wouldn’t crank. Then, with the battery just charged, I took the car to the San Diego British Car Day show, which included a 40 minute drive at freeway speed (i.e. more charging). When it was time to come back home, the car wouldn’t crank, but luckily, my portable jump started was fully charged and it saved me the embarrassment. I began to suspect the starter motor, so I checked the little blue relay input and output, but everything checked fine, so I was ready to have the starter motor replaced, but before that I decided to really check whether the battery was really charging fine, so I took the battery to the place where I purchased it and they did a full charge on their special machine, finding no problem with it. This here really made this, yet, more confusing. However, this problem kept going right on, so I needed to make sure about no current leaks so,to make it easier, I purchased a low range, clamp precision amp meter and started to work real hard on possible drain when the car was not running. To my disbelief, the meter read 30 ma at the isolated firewall left post circuit, plus another 33 ma at the firewall isolated right post circuit and another 38 ma at the isolated trunk floor post with the firewall posts disconnected. That was a total of 100 ma drain, no wonder that I was losing battery charge after a couple of days (or even just hours at the San Diego car show).

With nothing else to use as reference, other than suspecting a possible battery problem, I went reading a lot about what can defective batteries behave like, and I began to see the light. So, without fooling around, I went to another branch of the store where I purchased the battery from, some 5 years back (8 year pro-rate warranty) and the battery did not test right, so they gave me a somewhat generous pro-rate warranty refund with the purchase of a new one (the exact same Bosch unit). New battery: absolutely ALL problems disappeared like magic; finally I had a "normal" car... It was an internally defective battery what kept fooling me for several months. I’m still trying to figure out on a piece of paper where to where were those 30 ma flowing out from the battery because how can current be measured outside the battery (i.e. on the battery cables) if the drain is an internal drain (i.e. an internal short). I have electrical background but I can’t figure this one out… maybe some smarter member can see this better than I can and figure out those sneaky electrons' route...LOL

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Old 05-30-2019, 07:20 AM
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That 30MA is about normal for the radio memory, and in your case, the factory alarm system.

Depending on the "outgoing" circuits layout on yours, the black box for the alarm/security may be getting its power at that boot floor junction, or even before it. That is the case with my S Type.

Add to that, these "modern cars" do not go to sleep instantly you lock the doors and walk away, and I have NO idea on the 1994 in that area. The 2001 S Type takes 47 +/- minutes to finally go to sleep.

I used some 3mm wire, and disconnected the -ve battery lead, ran the 2 small leads outside the boot, one connected to the -ve post of the battery, and the other to the -lead away from the battery. shut the lid, and connected a Digital Amp Meter to those 2 leads, and watched.

7 minutes elapsed, 1.8amps
18 minutes elapsed, 1.1amps
27 minutes elapsed, 0.9amps
47 minutes elapsed, 39ma, and thats where it stayed.


If you open a door, coz ya forget something, the whole process starts again.


When it comes time to nod off, the system looks at battery voltage, and if its below 11.9V, the thing will NOT go to sleep and continue at 0.9 amps until flat, its that simple.

Gotta luv modern technology, at least my MK10 goes to sleep when I walk away, sweet.

All my cars (Jags) sit on a simple "battery Minder" when parked at home/storage, and my spending on batteries is now zero.
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Old 05-30-2019, 06:00 PM
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Now that you mentioned that "battery minder", I have used two battery maintainers (Black and Decker) on my two less-driven cars and, since the XJS is my show car, it is the car that gets less driven of all three, so it happens to be the car that has been connected to this device for much longer time than the other two cars (the XJR and the Z3) and I wonder if all this use is what actually internally damaged the Bosch battery. By the way, the battery on the Z3 died in January and the XJR's had to be replaced in March because of engine codes, plus battery age (but neither because of internal malfunction as the XJS battery did), so now all three of my cars have a new battery; is this a trend telling me something about battery maintainers? I dunno, but I stopped using them and I'm now using a great mid size device from Harbor Freight that has a 2 amp maintainer, a 10 amp charger and a 50 amp jump started that has been able to successfully crank no less than my V8 XJR. I could use this unit as a (2 amp) maintainer, as well, but now I prefer to keep an eye on the LED volt meters that I have plugged in all three cars' cigar lighter receptacles and wait for the voltage to drop to a little less than 12.5 volts, then I use this device's 10 amp charger mode to fully charge the battery. I've always been curious as to whether this constant automatic connection and disconnection by the maintainer once the battery reaches full charge is something that the battery cells simply don't like.
Old 05-30-2019, 06:53 PM
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For a long time my 95 was showing a flat battery after sitting for more than a week. The problem has gone away, I did multimeter test 2 years apart with the same results-no drain... I checked for no lights staying on or other drains. No drain anywhere....The only thing that has changed is that I am making sure I shut the trunk and engage the lock properly which seemed to not be engaging fully (thus potentially leaving trunk lights on) ,and also, I do not work at the same place anymore. This matters because my job was one mile away from home, and the car would literally be driven once a week, or less depending on weather, for one mile and back. The battery never had a chance to recharge at all.

I avoided battery chargers because I prefer for the car to work as intended. I was disconnecting the battery which was a pain because I would have to re-pair my phone to my BT system and set the clock every time I drove the car. I have now left the car sitting for over a week and it starts as it should. So pleasant to not have to reset clocks or stereos!
Old 05-30-2019, 08:16 PM
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Batteries in general do not like sitting around, they sulphate up and die a slow death.

When I was at Lucas, and the battery shop was in the rear of the building, and I am talking the early 70's, lead acid construction, and things have changed in batteries since then, a suspect battery usually got whacked with a rubber mallet a few times, and 80% of them rejuvinated within spec. Apparently this dislodged the "growth" on the plates, and all was well. Probably not going to happen with the new technology battery internals.

My minders are 650Ma, and the X300 battery is now 7 years old, and the car gets used 3 times a year if its blessed. The MK10 battery is 9???? I think, and that gets started once a year, maybe, when I remember I got the thing.

A 2amp minder could "cook" the battery, but again, technology is way beyond my grey matter now.


You do get dud batteries, right off the shelf, we get them at work semi regularly. Whenever I sell a battery, I always suggest the buyer charge that battery overnight, coz experience has proven the shelf batteries are NOT always fully charged, and the car alternator will not do it. OK, if he is in the carpark with a flatty, not going to happen, but later on, they can and usually will trickle charge that battery.
Old 05-31-2019, 01:03 PM
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Electrickery will defy me for the remainder of my days.

1. 30 MA discharge is minute. A sure clue of a bad battery. What else????

2. Got a chuckle as to the "whack" method, aka percussion maintenance. Knock the Sulphur deposits off the plates. Expose copper to the acid. Can be charged. deposits sink to the bottom and are harmless, for a time. As grant says, not any more, no room don there!!!

3. Son was over and accelerated my electronic cleanup here in my work room. Removed all the toys I more longer or seldom used. Two desk tops, printer, modem. phone, two lamps. Electric switches that power down all the way, past mere seep mode. Boot the computer and the stuff comes along. Modem, phone and cell charger always "hot".

Tried one on my cable box and TV. VIZIO howled loudly. Surge on repower. No, restored to as was.

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