Adding Another Group 31 Battery In Parallel

TonyG13

I've read through most of the archives regarding batteries and I am thinking about adding another Group 31 house battery to have two in parallel to increase my amp hours.

I know some will say go with AGM, but the cost to convert starting and house right now for me would be too many boat bucks, so sticking with lead acid for now.

Question involves charging. I have a Progressive Dynamics Intelli-Power Marine PD-2130 converter/charger.

If I  install the new battery in parallel with the existing, and wire as shown, will the charger distribute charge equally between the two? Or do I need to do something else? (Couldn't really find any info in the PD-2130 manual.)

And what AWG wire size should I use as the jumper between batteries?

 

MH342

The charger will treat them as one large battery.  It won’t know the difference because putting them in parallel as shown will increase the effective surface area of the lead plates to hold a charge. Also note in your diagram that it’s a good practice to connect the ground and power as shown … on opposite batteries. This way the round trip of current is equalized between both jumpers, and the charging voltage will also be the same to both. The only caution is that I’ve heard counting a new battery to an older battery can prematurely age the new battery, since it does a little more work as they are drained down. 

For jumper size, you can’t go wrong with the same size or similar as the main leads.  Any lead in the path should be sized for the breaker of fuse that protects it. You can find premade leads online and the price difference isn’t much between sizes.

You will enjoy the added capacity, and it may extend their life because they won’t be discharged as deeply. Good luck!

TonyG13

Thanks so much for the concise info that I could understand (since I'm 12V electrically challenged)!

YYZRC

I did this on my 330 with lead acid and it was great. Just match the existing battery cable weight (I think mine are 1/0). 

oscar1

First, I did it using two AGM batteries with the same charger as your, but after a 6 month of used it,  the charger was not able to keep demand for the 2 group 31 house bank, plus the engine started batteries which are group 31 as well, so I install a new 50 amp master volt charger plus bigger size wire to accommodate the new charger and My problem was gone and now my batteries banks are always full of juices.