Battery Upgrade

by Greg Zimmerman

It was time to upgrade the battery and I wanted more capacity without jumping to a group 31 which requires modifying the hold down (they’re really big and heavy). Trojan batteries are made in the USA. They normally supply much larger batteries for golf carts, mega yachts, and big trucks. Trojan batteries need to be ordered from a dealer- find your nearest by clicking here.

UPDATE: I now recommend the Trojan 27-AGM battery as it’s sealed and maintenance free. It cost more, but it’s worth it. If you’re up for a challenge and need the capacity, you can use the bigger AGM-31, but you’ll need to modify the hold down bracket for clearance. No need to cut the terminals on the AGM either.

Another option is the much cheaper TMX-27 wet cell. It has more capacity, but needs distilled water added every 6 months. To fit it, we need to cut off the threaded post on the terminals because they stick up too high to fit in the battery compartment. A pair of off-set terminals are used to give the required clearance.

TIP: Don’t forget that the white and green wires are negative and the black is positive!

The TMX-27’s capacity at a 20 hour discharge rate is 105 amp/hours which is quite a bit more than the 87 amp/hour rating of the original Interstate battery. The AGM’s capacity is 88, pretty much the same as the original. I also recommend the Little House Custom Battery Disconnect, click here for the article on that.

Just fits!


Gary Wells January 28, 2019 - 12:01 pm

Great job on the battery change out. What size wire from the battery to the distribution posts. And the batter disconnect (RED) block – what size? Or were these items already on the Casita?


Greg Zimmerman January 28, 2019 - 1:09 pm

It’s 8 gauge wire. It was included in the Little House Customs battery disconnect kit along with the terminal block and connector.

Gary Wells January 31, 2019 - 12:39 pm

Thanks Greg.

Kirby Gchachu June 2, 2020 - 8:24 am

Thank you for this information. Your article gives me expected roadblocks to deal with & I appreciate that.

Steve Hilliard June 27, 2020 - 8:25 pm

Hey Greg, I just noticed something in the bottom of the last photo–is that a remote thermometer?

Greg Zimmerman June 28, 2020 - 9:17 am

Good eye! Yes it’s one of 3 accurite thermometers I had. One in the fridge, one in the freezer, and the battery cave was the best place I found to get outside temp.


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