EarthX battery and gain some useful load. The factory battery for most Rotax powered planes is an Odyssey PC680. They last a couple years and is what is recommended. I had an auto part store battery in my Evektor.
Are you an S-LSA? In that case, you need a Letter of Authorization from the manufacturer to install any battery other than the one installed at the factory.
Edited to add: I see Samuel has you covered for the Odyssey.