Thread: Flat battery - dual battery system?

Originally Posted by Pedro_The_Swift

but is it working?

Bastard!




The lights come on.

Originally Posted by drivesafe

Hi again Ron, I just read waynep’s post and that reminded me to ask you to check your voltage at the cranking battery after you have driven the RR for at least 15 minutes.

Say, next time you go to work, pull up and leave the motor running.

Pop the bonnet and see what voltage you have at the battery.

Measure at the battery terminals, not off an earth point in the engine bay.

Some of the Discos run at 14.7 volts and this really makes a difference at keeping the battery in a better state of charge.

Your RR may be running at a much lower voltage and this can easily cause the sort of problem you are having.

Just another suggestion.

Yes, I'll do that. The RR does a run a lower voltage than later cars designed for calcium batteries. This is the second or third calcium plus a new alternator in the RR (in nearly 7 years) - plus two in the Disco (in a year). I won't buy another calcium battery for the P38A.

Originally Posted by p38arover

I won't buy another.

You won’t buy another Alternator or another LR

Originally Posted by drivesafe

You won’t buy another Alternator or another LR

Calcium battery.

I checked the voltage at the battery terminals when I arrived at work - engine running 13.6 volts.

Hi mate and there is your problem.

At 13.6 volts, you are only ever recharging your batteries to about 75 to 80% each time you drive and your batteries are never fully charged, no matter how long you drive for.

This is a sure fire way to shorten any type of battery’s life.

13.8 volts is the absolute minimum voltage to be able to fully charge a battery and even then, it will take a lot of driving time to achieve a fully charged battery.

Before you do anything ( other than hooking up your battery charger whenever possible ) find out if you can get your regulator adjusted up to about 14.2.

14.2 volts is a good optimum level that will get your batteries fully charged in a reasonable time but will guaranty not to over charge them in hot weather.

Again, before you do anything, get your batteries on a charge. The sooner you do it the more chance you have of maintaining the batteries you have.

Again, keep us informed

Are regulators adjustable these days?

Originally Posted by p38arover

Are regulators adjustable these days?

That one I can’t help you with!

Oh, I forgot to mention the ambient temp was 36 deg C. Based on my hazy recollection of lead-acid battery charging, one should reduce the voltage as the temperature rises - negative temperature compensation.

I'll take another measurement after my run home after work about 11.30pm when it will be cooler.