Adding more battery capacity in limited space

pauldub wrote:
What is the downside of using a Trojan T-1275 (12 volt) along with a pair of T-105s (6 volt)?

A pair of T-1275s will give you about 300 Ah of power compared to about 225 Ah for a pair of T-105s (or any other GC2 battery). The cost of a pair of T-1275 will make you want to cry !

pauldub wrote:
Maybe someone has some good suggestions about ventilating a battery box. Please don't suggest that I use AGMs at triple the price of FLA.

Get a round vent from Home Depot and drill a hole.

The most COST EFFECTIVE batteries are standard FLA 6V golf cart batteries like the T-105s (the ones at Costco or Sams are MUCH cheaper than genuine Trojan). Change to anything else and the cost goes through the roof.

Our C has an 8D size battery box (that can take two normal batts instead) inserted into where it goes under a dinette seat where the power centre/converter also is. That battery box has an outside door and is vented.

Below that is a compartment also with an outside door. I drilled holes in the battery box floor going down through the RV floor into the lower compartment where I can carry more batteries that are "outside". Wires go from "upper bank" to "lower bank". Needed three holes for balancing the bank to not have the upper bank be "upstream".

Later, I went AGM and now have an actual 250AH 8D AGM in the upper box and keep two 100AH AGMs inside nearby banked as 450AH. If I need more battery, I can still put some in the lower compartment.

You don't mention what chassis your C is built on. Mine is on a Chevy pickup chassis, gas engine, and under the hood there is a second battery shelf (currently empty) where a diesel's second battery would go. If you have a similar setup, could you add a 12V there?

Tigers also sometimes add a battery area under the floor by the rear axle. Could you do that?

An alternative solution when space is tight is to look into AGMs that can be installed in different orientations. We have a test cart at work that has 16 Group 31 AGMs in series/parallel combination mounted standing on end back to back in two rows of 8. Bunch of power available in a 5'X2'X13" space.

I'm not a big fan of AGMs from a power density perspective, but the versatility they provide with mounting position is a a big help sometimes.

If you have some extra available height, but not floor space, look at the Trojan 6V T125s. They're a slightly higher battery with a higher rating.

Bill

I got two used T-1275s in 2013 that had been in a golf cart for two years and were no longer considered worthy for that job. I did the "recovery" stuff (equalized etc) and got them back into decent shape. They lasted till early this year doing all kinds of 50-90s and high amp fast recharges etc. like I do.

I had the two T-1275s in parallel in parallel with two 6s in series as the usual set-up. Worked great. The T-1275 has big holes for the cells, like a 6 does, unlike the 27s with those tiny holes. Means they recharge nicely like a 6 does with bubbles and the SG comes right up like it is supposed to, same as a 6.

My two 6s at the time were Interstates and also a pair of Exide 135s. Sometimes I went with six batts: the two T-1275s and the two pairs of 6s, wired up as three big 12s.

You can't go wrong whatever combo you go with. T-1275s are a good RV battery for deep cycling and fast recharging, same as a 6. With T-105s they have the same charging specs too.

Meticulously audit the manufacturer's recommended voltages for charging and float before you leap. Temperature plays into this so look at 0F as well as 90F

Do the two values agree? Is the spec specific gravity the same between both batteries?

If yes to all, go for it.