Some battery compartments can take a pair of Group 31 batteries, my under the step compartment in my Axis can. The overall length of a pair will be 26". G31s give you about 25% more Ah capacity- 100 Ah each and they usually aren't more expensive than G27s. Renogy, WindyNation and others sell G31 AGMs on Amazon for about $200 each.
But you may have a problem with the existing cables, particularly the jumpers being too short with G31s. Easy to fix though.
David
__________________
|