Axillary battery

Happy Halloween everyone!
As the new guy on the block, I enjoy reading all the responses of the forum about Motorhomes, trailers, tow vehicals, and much more information. I have a question to all of you Mummies and Frank Instiens out there. I have a Prowler 300FQS and would like to install an 12v axillary battery for additional 12v power. How do I hook up the batteries together so it isn't 24v? Your response would be much appreciated.
Thanks so much for all your suggestions. :laugh:
Axillary battery

Place the batteries side by side. Make sure positive post is on the same side (right or left) as you are looking at the batteries.

Take 2 jumper cables and hook the positive post of your NEW battery to the positive post of your EXISTING battery.

Hook the cable to the negative post of your NEW battery and then hook that cable to the negative post of your EXISTING battery.

You will still have 12 Volts DC - but with substantially more reserve.

Remember your battery charger though - it now takes a lot more to re-charge or maintain a charge (after all you have double the battery).

Good luck - God Bless.

Bill & Judy

Axillary battery

Thanks alot, You have really been a great help. So. . . it is pos. to pos. and neg. to neg. I've been s-o-o-apprehensive to connect the batteries this way, would a battery isolator help :blush: ?
Thank you
Axillary battery

Yes - Maybe. The big advantage a battery isolator would have is that IF you disconnect the extra battery from the main one - and the main one is discharged - then you can turn on the extra battery and still have power (unless the main battery shorts out or destroys itself).

Simple really - but I understand your apprehension.

Axillary battery

Generally, batteries should be same type and age if you are planning to do this. I recently switched house batteries to AGM (absorbed glass mats) at a higher cost however they are no maintenance and no worry of lead plates coming loose on rough roads. Also much deeper reserve. :laugh:
Axillary battery

Hey guys there is something about a battery system you should know. You must get a battery insulator switch because it you shut down everything with the two batteries hooked in parrell they will begin to fight each other and end up dear as a Mackrel (I can't spell).
What happens is that the stronger battery will charge up the weaker but it is never EXACTLY equal so then the other battery will charge back the other way. Sounds strange but that life.
Axillary battery

In essence - that is connect. No 2 batteries are exactly the same and the only way to maintain 2 batteries fully charged - without problems - is to supply them with a trickle charge at all times (a solar cell charger will even take care of the problem).

Bill & Judy
Axillary battery

Four 6 volt batteries have been used hooked up in parallel since the 50's in semi trucks with 24 volt starting systems, and I've never heard of them fighting each other, exect when one shorts out.


Senior Member
Axillary battery

umm, paul? 4 6 volt batteries would have to be hooked in SERIES to get 24 volts out... In series, the batteries are strictly additive, and cannot affect any of the other batteries under any circumstances, even shorting out. Of course, one battery shorting out would provide only 18 volts to the circuit, which the circuit would not like.


Senior Member
Axillary battery

Parallel batteries do not "fight" with each other, whether connected to a load or disconnected. RVs and many other uses have had batteries connected in parallel with no isolator between them for many years and not one fight has beed documented! After fourty years of working with electricty, I have no idea what Poppa is thinking of, or where the information came from?

There is very little value to having an isolator between the batteries unless something unusual happens to one of the batteries. Very few instalations have an extra isolator between them. Many RVs used for dry camping have solar chargers and use six or more 6V batteries wired in series pair and the three pairs in parallel. It is rare for any of them to use isolators.