Thread: Help, please. Second battery for LR

A simple option for you

buy a 12V blender

The 12 Volt Shop

This is the way I did mine.

My 'switch' is auto on voltsensing - when the voltage of the main battery drops below 10.5 v (+/-) it isolates the main from the 2nd.

Or as mentioned above you can get a large manual switch - they use them on boats , some are just off - 1 - 2, others go from 1 batt - off - 2 batt - off - both batt.

Originally Posted by popotla

I haven't got a scanner to hand, but here's a description of the circuit as it's been wired.

Cable from + terminal of batt #1 to + terminal of batt #2

Cable from neg terminal of Batt #1 to chassis earth

Cable from neg terminal of batt #1 VIA CUT-OFF SWITCH to neg terminal of batt #2

That's it.

From what you have typed above - your accessories will still continue to work, difference is it will draw the power (and complete the circuit) through the first battery.

The second battery won't have any play in this, as it is isolated. Once hooked together they are basically in parallel - another words still 12V, but the amp hour is doubled in effect.

Problem with this set-up is that you can't isolate your first (starter) battery at all. This means that if you pull up to camp for the night, then the first battery will be supplying the power for everything. And in the morning you will be relying on your second battery to start the vehicle.

Another thing to consider is when you turn the isolator on, both batteries will try and equalise themselves (for lack of better words). This is why those of us that have gone down the manual switch route have used the marine isolator - it gives us the option to choose which battery to use, and to effectively isolate whichever battery we want when camping etc.

Personally speaking - the above set-up completely negates the primary reason for having a dual battery system. You may as well have two batteries in parallel permanently.

Cheers
Chris


P.S - of course all of the above goes out the window if it is a positive earth vehicle!

It's a negative-earth vehicle, with the cut-off switch now in the + cable.

I forgot to mention that four sockets are connected to the terminals of battery # 2. Sorry for any confusion.

Another thing to consider is when you turn the isolator on, both batteries will try and equalise themselves (for lack of better words).

** I take the above to mean that when the two batteries are linked, after power has been taken out of batt #2 overnight, say, power will flow from batt #1 to batt #2. Does this matter? What practical effect does it have?