VN Keeps Killing Batteries?

[DarrenF]

Sorry I probably should have explained better. While the car is running I get practically the same voltage from the alternator as I do from the battery. When the car is turned off it falls down to 13.5 volts at the battery within a few minutes and stays stable at 13.5 unless I draw any power with lights or other accessories.

I tried your tests with a jumper cable without any measurable change from this.

I've been using 650/700CCA batteries. I'm not sure of their RC rating off the top of my head.

I'm starting to think I've just had bad luck with batteries, across brands somehow. Seems unlikely however.

 

[stockies]

Have you checked if the boot light is turning off when the boot is shut? - Just open the ski hatch in the rear seats and see,
Does the glovebox light turn off? or in addition is the plastic around this light look melted, or is warm?

I'd also be adding another earth strap from the negative terminal of the battery to the ground bolt next to it. Seems to help the lights when the voltage drops due to idling and aircon being on.

 

[hi_ryder]

ive never had a battery read over 13 before, usually 12.5 on my cars. for the sake of $50 id just replace the voltage regulator on the alternator. your problem could be as simple as that...

 

[Immortality]

Agreed, a fully charged battery should read 12.7-12.8 volts max. They do read higher just after shutting the engine down but it should settle to high 12 volt range after a while.

My old VN had about a .5 volt drop between the alternator and the battery. Charge lead was good, the drop seemed to be in the earth cable. What I have found with many V6 engines that are older is that you can get oil under the main earth cable lug which can act as a potential isolator. I added another earth cable from the alternator directly to the battery and that brought battery voltage to within .1-.2 of the alternator which was putting out ~14.3 volts with a few revs and full load.

 

[DarrenF]

Thanks for the replies everyone. I've just gone and performed the following:

- Removed boot and glove box bulbs. They weren't warm or melted, I couldn't see any evidence that they were on but just in case.

- Added another earth strap from the negative terminal of the battery to the ground bolt next to it.

- Replaced the voltage regulator.

- Rechecked my battery voltage after engine shutdown. It actually reaches 12.7 within about 30 minutes and levels out there.

If this works I guess I'll put it down to the voltage regulator. Cheers for the suggestions everyone. I should be picking up my new VF very shortly anyway

 

[Immortality]

Battery volts sound spot on now.

I guess time will tell

 

[hi_ryder]

+1 for above comment ^^

its the first thing i do when buying a run around vn vp. i dont even test to voltage regs, bin them and buy a new one. that little item can cause so many problems. 90% of the time the brushes were so short they'd have been due soon anyway.