Thread: Dual Battery Wiring

Geez there seems to be some confusion in this post.

Firstly the BATTERY is in the boot, so the wire gauge is related to the maximum input the second battery will get from the alternator when it is flat and the alternator is charging away at full noise trying to charge it. The wire gauge may affect the voltage into the second battery and therefore its recovery time.
I this case the draw of the accessories is less/not relevant.

Second the chassis is not the best place to earth to , as the earth points and the starting battery are usually earthed to the body, not directly to the chassis. Bodies are rubber mounted and the only link is often corroded body mount bolts. AFAIR the poster has not said what car but if a D2 it is a welded structure, there will be earth points all over the place, and IMHO a complete earth link is not needed, although if you have a 2B&S input it may be desirable to have a direct earth connection.

If your controller light is on, there is a fair degree of certainty that the second battery is being charged.
What led you to believe that it wasn't?

Regards Philip A

Originally Posted by PhilipA

Geez there seems to be some confusion in this post.

Second the chassis is not the best place to earth to , as the earth points and the starting battery are usually earthed to the body, not directly to the chassis. Bodies are rubber mounted and the only link is often corroded body mount bolts. AFAIR the poster has not said what car but if a D2 it is a welded structure, there will be earth points all over the place, and IMHO a complete earth link is not needed, although if you have a 2B&S input it may be desirable to have a direct earth connection.

If your controller light is on, there is a fair degree of certainty that the second battery is being charged.
What led you to believe that it wasn't?

Regards Philip A

Yes the 2nd battery is earthed to the side of the body behind the rear seat belt. The deep cycle battery sits in a case with an indicator of charge & it has gone flat without use which is why I assume it has no charge.

Yes the 2nd battery is earthed to the side of the body behind the rear seat
belt. The deep cycle battery sits in a case with an indicator of charge &
it has gone flat without use which is why I assume it has no charge.

Hmm.Have you checked the voltage of the second battery with a multimeter with the engine running?Should be around 14.6.
Does the battery enclosure have a gauge which takes current to operate?
You can measure by putting a multimeter across the +or -, and that may tell you if there is current leakage somewhere.

And finally , how much do you drive the car and how old is the battery?
Regards Philip A

No I need to do that, had the battery out to charge it up on the charger.

It just has a 3 light check button on top of the case that you press, no voltage loss there I wouldn't think.

The battery is over 4yrs old now. It had extended periods of low charge in a van I previously owned & probably doesn't fully charge anymore. I can't see the white bubble through the viewing hole, just black but it charges up still on a charger.