Adding another battery

[JerryB13]

Hello all, I hope everyone is enjoying the season so far. I am adding another battery (deep cycle marine) to my Jayco jayflight 28bhbe. Just double checking I can get 2 new battery wires and go pos to pos/neg to neg on the 12V to connect the 2 batteries. Do I have to add any switches for this to work or not ruin my electrical system. I prefer not to add any switches or cut offs if not needed and just run with the 2 batteries connected. Thoughts?

[clubhouse]

You plan is correct; + to + and - to - for 12v batteries. The addition of a switch to cut off, or isolate, the batteries for the TT are convenience items that folks have to eliminate phantom drain on batteries. The exactly same thing can happen by disconnecting batteries to pulling the 30a fuse on the + wired from the battery to TT.

I have dual grp 24 batteries and no disconnect switch. I pull my batteries when not in use and keep them on a battery tender in my garage.

[Scoutr2]

You need to ensure you are wiring them in parallel, and not in series. Here's a diagram:


This should greatly extend the time you have 12V available for camping. Be sure your second battery is of the same group number. It's not mandatory, but the same number of plates, etc are recommended.

A disconnect switch is a good addition - on the negative (ground) side of both batteries. Disconnecting them prevents them being discharged by small parasitic draws, such as your propane leak detector, sound system, etc.

[JerryB13]

Thank you thank you clubhouse and scoutr2

[mike837go]

Also, be mindful that the two batteries are closely matched.


A run-of-the-mill automotive battery paralleled to a deep cycled battery will drive your charger nuts and not allow the deep cycle battery to charge properly.

[scrawf7]

Originally Posted by Scoutr2

You need to ensure you are wiring them in parallel, and not in series. Here's a diagram:


This should greatly extend the time you have 12V available for camping. Be sure your second battery is of the same group number. It's not mandatory, but the same number of plates, etc are recommended.

A disconnect switch is a good addition - on the negative (ground) side of both batteries. Disconnecting them prevents them being discharged by small parasitic draws, such as your propane leak detector, sound system, etc.

Is there a reason you recommend to put the cut off switch on the negative side? When I installed mine I put it on the positive and haven't had any problems with it. Is it something I should go back and change?

[mike837go]

Originally Posted by scrawf7

Is there a reason you recommend to put the cut off switch on the negative side? When I installed mine I put it on the positive and haven't had any problems with it. Is it something I should go back and change?

Only from a maintenance/safety perspective.

All those potentially bare connections that may have to be serviced during the life of the RV. If they are at the same potential as ground, there is much less likelihood of shorting/sparking a tool when having to repair or replace the connectors or switches.

[Subaru297]

The new battery should ideally be identical to the first battery. Same brand, model, age and capacity.
Putting an old used battery with a new battery will shorten the life of both batteries. When using multiple battery banks it is best to get them all at the same time and same age. Otherwise the different aged batteries will charge/discharge at different rates and won't balance properly.
If you still do this make sure both batteries are both fully charged before connecting them in parallel otherwise the charged battery will dump current into the discharged battery really quickly.

[Scoutr2]

Originally Posted by mike837go

Only from a maintenance/safety perspective.

All those potentially bare connections that may have to be serviced during the life of the RV. If they are at the same potential as ground, there is much less likelihood of shorting/sparking a tool when having to repair or replace the connectors or switches.

Also worth noting - unlike your tow vehicle:

- The BLACK WIRE is POSITIVE (+)

- The WHITE WIRE is NEGATIVE (-)

I've forgotten the explanation for why the RV industry does things this way, but unless you are aware, you could damage the trailer electrical and charging system by hooking up the battery backwards - not to mention the battery. (I'll bet this gets REALLY confusing on a motorhome, that has both systems on-board the same vehicle!)

[mike837go]

Originally Posted by Scoutr2

I've forgotten the explanation for why the RV industry does things this way, but unless you are aware, you could damage the trailer electrical and charging system by hooking up the battery backwards - not to mention the battery. (I'll bet this gets REALLY confusing on a motorhome, that has both systems on-board the same vehicle!)

Because in house wiring neutral (white) is at the same potential as ground. The 110V wiring in the RV follows that pattern. With Black and/or Red being HOT.

So, when wiring the 12V side, white is ground, negative, etc. Usually black is hot, +12V, etc.