I needed the weight of the battery in my RV-6 to keep CG where I wanted it.
Concord makes the
AGM-1234T Chairman battery and it is the same size, weight, and spec as the
RG25XC. The terminals are reversed and the battery terminal screws are a different size. The Positive and Negative terminals are reversed on the Chairman battery. The Chairman battery is 1/3 the price of the RG25XC.
IF you have enough battery cable that you can cross the terminals, the AGM-1234T can be used to replace the RG25XC. This is the
outfit that had the best price / deliver schedule when I needed my battery replaced earlier this year.
Spacers work on the PC-680 battery in the battery box like others have said. The PC-680 will also save you some weight and you will only give up a little (~7) Amp-Hour capacity.