One of them I modded a long time ago and it worked great. The mod is super easy if you can solder or have experience splicing wires etc.Following for updates on the modded Ecotech battery. Mine died and I plan on swapping it out and turning it into a project myself.
Happy to help if/when you're ready.
The main "problem" is finding a good battery that fits. The batteries I used aren't available on Amazon anymore but with some Googling etc you should be able to find one (or two wired in parallel) that fits