Battery problems
 

I have been having battery problems for ages on the XK8 and, as you know, when the voltage drops too low all sorts of odd things happen. I know that I need about 13 or 14 volts in the battery, but keep losing volts and going down to 10 or 11.

I decided to try and sort this once and for all, and I figured that I needed a battery with more capacity to make sure that I don't keep getting these problems. So I found a 24volt battery for a decent price and fitted that, knowing that I'd have at least 10 extra volts in reserve.

But now I'm just getting a load of other problems - the car won't start and I get odd warning lights. I've checked that the the full 24volts are getting through to the connectors under the bonnet, and that all seems fine. I wonder whether the starter motor might have coincidentally gone bad?

It sounds like the Starter Control Module has detected the over voltage so won't engage the starter motor to avoid damaging it. Hook up your code reader and see what comes out. You should get a P1111 which indicates all tests complete, plus a P0104 if the SCM has shut down the motor. I think the US spec cars have a P0401 for the same code.

Best of luck, keep us posted.

Maybe it will sort itself out on April 2.

Damn you!!!

Sorry to say, but don't think the 24V was a good idea. Just the lights blowing would give you the indication that all was not right.

Can't blame you for trying a 24V battery, but I tend to agree with CJD777 that it probably wasn't a good idea. Especially with such a voltage sensitive car model.

Maybe the best way forward is the standard stray current check with just the regular 12V battery to see where/if your voltage loss is coming from.

With just a 12V battery, open the boot and lock the car. Leave standing for a while, put a standard voltmeter across the battery cable ends, and read the mA draw. If it's more than about 100mA you've a drain. Start pulling fuses to see what system is causing it and it's usually a bad ground somewhere that just needs cleaning up.

Not on my Jag, but on my 1970 Triumph GT6, I cleaned up both ends of the battery terminal cables, sanding and medical alcohol in those days, and used silver conductive paste on the body contacts.

I find it hard to believe that anyone would put a 24V battery in, but then it is April 1.

Yep, clearly an April Fool's prank....

Just realised.... you boys are too quick for me
 

Geez. We don’t really have April’s Fools day here in Bahrain but still....

i bit hard too. LOL!

Can you even buy a 24V battery?

Lorries use 24v, but only an April Fool would fit one to a Jag!

Hehehe
 

At least today I learned that HGVs have 24V batteries.

Still can’t believe that I didn’t get the joke