Battery Charging
 

Is it Okay to charge the battery from the + terminal in the engine compartment. Seem to recall reading that JAG say remove battery.
Thanks,
George '03 XK8 UK

With all the computers aboard a modern car it is always best to charge the battery disconnected. That prevents any voltage spikes from frying something expensive.

That being said, it is certainly possible to charge the car from one of the B+ terminals under the hood. They are merely cable extensions of the battery post passing through a couple of 250 amp fuses.

Camgear, if you are going to charge the battery while in the car, use the 2 amp setting, not the higher 10 amp setting. THis will help minimize the spikes that you can possibly get. The odds of getting a spike big enough to cause damage is pretty unlikely. If you live in town, the likelihood of a spike is even smaller. If you live in the middle of BFE, then getting a spike is more likely. So, if you are like 99% of the people out there, charging the battery with it in the car should be no problem.

I have charged the battery while in the car several times now (via hooking the charger cables directly to the battery + and - posts without removing any other cables to the battery). I have gotten in the habit of doing this with almost all or the cars I have owned maybe once every month or so just to make sure the batteries are fully charged. The charger I have is 10 or 12 amps but adjusts down to a trickle based on the battery charge.

Yes I know that it is best to unhook the cables first and/or hook the negative charger cable to the frame rather than to the post. But I am lazy and have been doing this for years now without any problems. Of course I keep the ignition key turned off. Again, done this with a variety of different cars and NEVER a problem.

Doug

Thanks for the advice guys.
George

Battery Chargers
 

Battery chargers come in different flavors. The really old ones used crude methods (relays and resistors) that apply high voltage to get a quick initial charge and then back down in one or two stages if they back down at all. I worked at a garage when I was in high school and we had a charger that would shoot acid out of the caps. This type of charger can be deadly to the electronics.

Modern chargers use current control to charge at a controlled rate depending on how far down the battery is. The battery manufacturers publish ideal charging curves, to get the fastest charge with no damage, and the good chargers follow this. This is why there are often selector switches for the types of battery (AGM, Sealed, Deep Discharge,etc) as each has a unique ideal charge curve. Most chargers these days have a microprocessor that manages the charge curve.

The small maintainer units are only capable of low charge rates and are safe for all batteries. They are intended for counteracting self discharge and ambient loads like the security system, radio backup, ECU backup, etc. Most modern electronics are always on at a low level so they can react instantly rather than do a boot up when the key is turned. If the battery is not maintained it will discharge in a couple of weeks so it is a good idea to use a battery maintainer if the car will not be started at least once a week.

I've most always charged batteries in cars without removing +/- cables.

Charged battery with cables connected in my 2000 XK8 convertible a month ago... No problem.

Charged it yesterday with cables connected... Now it cranks strong but will not fire... not even a hint it wants to.

So... Now I'm chasing issues. Never again without removing both cables.

The starting problem has nothing to do with how the battery was charged. The alternator can put out over 100 amps, so a 20 amp charger is 'nothing'.

One caveat ...

Charging with the cables connected is in itself not a problem. But making and (especially) breaking charger connections IF the ignition happens to be turned on ... this could lead to trouble.

Maybe a 4.0? May be bore wash if so.

That's a good point... does it spin more easily than normal like there is no compression?

Yeah... It's a 4.0. Seems to crank more easily and quickly... What's bore wash?

In short, if you start the car and don't warm it up enough before shutting it down, the raw fuel can wash the oil from the cylinder walls causing it to lose compression, thus no starting.

JagRepair.com - Jaguar Repair Information Resource

Link is from the DIY sticky thread :
https://www.jaguarforums.com/forum/x...ts-data-29800/

Guys i was thinking about this today. Looks like a perfect place to ask.

If you have bore wash, it was caused by gas washing away oil right? Can't just crank it because that adds more gas extending same problem.

Crazy question - could you disconnect the fuel pump fuse. Then cranking will first eliminate any remaining gasoline in the cylinder, while the normal 4 cycle lubrication distributes oil. Since no gas added with fuel pump fuse pulled, could this regenerate the oil / compression seal needed without pulling plugs etc.?

Seems like a hell of a lot easier than injecting oil. Would it work as a short cut?

It is charging, But says "Battery Not Charging"
 

Hello everyone! Hope you are well! Just put a rebuilt Denso Alternator in my 1997 XK8 part # LNC 1800AA. The Original Part # was LJA1800AE. The Alternator IS putting out. But the message on the dash says "battery Not Charging" The Amp gauge is also lit up. Now the heated seats are inop. No lights on center console work. Window goes down upon opening. I am TOTALLY lost here. This Jag is handing me my butt. Tried to do a hard Reset and Nothing. Any ideas would be appreciated. have a nice weekend!

MIKEY......Yes an alternator can supply 100+ A but thats for things like wipers /lights/fans etc not the battery where the charge current will not exceed 20A.
Please don't spread false information/Concepts

That's a 7 year old post - but what is wrong with it do you say?

As it is written it seems OK...

It is indeed an old post and you are right that it was correct all those years ago. A 100ah battery which is relatively flat will take a lot more than 20 amps.

Richard