Adding a second battery

How hard would it be to add a second battery in synch with the first one? Would two batteries provide twice the service? Would the charging system work with two or would there have to be modifications? Any thoughts?

[MudDog]

For understanding batteries and all of the options, this (12 Volt Side of Life) is a good place to start.

[Bill]

I highly recommend the book that MudDog mentioned.

A quick answer to your question is yes, you can add a second battery, and yes, it will about double the service time, and yes, the existing charger will handle it nicely, if a bit more slowly.

There are some subtleties. Batteries should be the same kind, and the same age. You have to choose whether you want to end up with two 6-volt batteries in series, or two 12-volt batteries in parallel. The book will go into all of this.

There are also a number of threads on this board about adding a second battery. I recommend you scan the thread titles in the Electrical Forum, and use the Search engine, to turn them up.

Bill

Wow, that was a fast response. Thanks, I will follow your advice.

I believe that two 12 volt batteries in parallel will actually provide a bit more power than you would get from having used them one at a time.

I added a second battery to my TM when it was new. I use a pair of group 24 12 volt batteries.

I have determined that I can not use a taller battery, because my batteries are on the tongue part way under the front of the shell because I have a wing away tongue. So I can not us the popular Trojan T105s.

I have room for a pair of group 27s, but not a pair of 31s. When these fail I will upgrade to the group 27s.

I added a switch on the outside so that I can choose any one battery, both batteries or no battery.

[Caver]

Two weeks ago I replaced my two "dead" 5 year old Interstate Marine Group 24 batteries with Magna Power label AGM Group 31 batteries (see the attachments). These are rated 105 AH each at the 20 hour rate. After years of adding water to the batteries a few times a year I was ready for maintenance free batteries. I selected these because they were available locally at a fair price. However, you have to pay a premium for the maintenance free batteries compared to the flooded lead acid batteries.

Two of these Group 31 batteries easily fit on the front swing hitch assembly with room to spare. I used the Walmart Large battery boxes.

I've only been on one four night outing with these but it was nice to know that I had that amount of reserve capacity. On sunny days the solar panels had them fully charged by noon. I setup my Morningstar MPPT controller for AGM batteries and monitored the charge modes as the controller went through multiple stages of charging. It ended up each sunny day with a float charge at a relatively low current into the batteries. I hope this gentle charge/maintenance operation provides at least five years of service. With the Trimetric monitor, I try not to discharge the batteries to less than 50% of the battery capacity.

These batteries are made by E.P.M. Products. The part number is 8A31DT.

There is a useful document on the Eastern Penn web site that discusses their AGM vs. Gell Cell batteries and includes detailed charging information as well as rated charge/discharge cycles:

http://www.eastpenn-deka.com/assets/base/0139.pdf

I'll provide a report on these batteries in about five years.

Ray