Thread: dual batt, primary 2ndry, how do i tell?

Hi Dave
The aux battery will be a deep cycle while the main is a cranking one . Look for amp hour and cca ratings on them . Accesories should run off the aux battery .
Cheers

Do you own a multi-meter? Necessary tool to properly answer these questions!

I could take a stab in the dark and say if you are standing at the front looking at the engine bay, the starter battery is on the left and aux battery on the right. This would be a standard layout for a D1 assuming an early '92 is the same as a '95 engine bay layout.. (anyone?)

Driving lights should go to main starter battery.
Lights, fridge etc should go to aux battery.

You should also see if you can find a battery separator. If you don't have one, then no matter where you connect accessories, they will drain both batteries. (Typical common set up has a separator).

I think the easiest way would be Main/Start battery is the one that
a) Has a power cable running to the starter motor
b) A cable from Batt positive to the fuse box in the engine bay (Drivers Side)
c) A cable from the rear of the alternator to the battery positve

And as Judo has said if in a D1 should be on the drivers side and multi meter to check if batteries are charged/charging.

Most dual battery isolators will charge the main battery first before switching to the aux so check the voltage on each just after starting.
I'd agree with Judo though that its most likely the one on the left when standing in front as this is the case with mine.
There should also be at least two cables on the positive terminal of the main battery and I think one goes to the starter motor.
Cheers
Mark

Originally Posted by Discomark

Most dual battery isolators will charge the main battery first before switching to the aux

Hi Mark and this is actually not the case.

I know if you will see a lot of the ads for different brands of isolators, where they imply that their isolator “waits” till the cranking battery is fully charged and then they start charging the auxiliary/house batteries.

This is nothing more than deliberately misleading ad hype.

There are one or two VERY expensive isolators on the market that do actually allow the cranking battery to charge before they start charging any auxiliary/house batteries.

All the standard isolators do nothing more than turn on once the alternator is up and running and have absolutely no idea whether the cranking battery is fully charged or if it just had enough in it to turn the motor over.

Hi Dave and this chart will let you know if the batteries have been charging while you drive.

The best time to take the voltage measurements is in the morning, BEFORE you start your motor.

Once you start your motor, you can again measure the voltage at both batteries and there should be at least a 1 volt increase at each batteries terminals over what you measured before you started the motor.

The increase voltage only means you are getting a charging voltage at the batteries, but the voltage you measured before the motor was started is a better indication as this shows if your batteries are holding a charge.

Also, try & keep something running off the house battery so there is a bit of a load on it. Batteries don't like being continually charged without a bit of drain & it will shorten their life apparently.
Steve

Originally Posted by Judo

Do you own a multi-meter? Necessary tool to properly answer these questions!

I could take a stab in the dark and say if you are standing at the front looking at the engine bay, the starter battery is on the left and aux battery on the right. This would be a standard layout for a D1 assuming an early '92 is the same as a '95 engine bay layout.. (anyone?)

Driving lights should go to main starter battery.
Lights, fridge etc should go to aux battery.

You should also see if you can find a battery separator. If you don't have one, then no matter where you connect accessories, they will drain both batteries. (Typical common set up has a separator).

excellent, thank you so much. ill get right on that.

cheers.

dave.