There are multiple lithium installs that are proven . The extended range batteries that I run are also in multiple other Gems and everyone has similar results . 50+ mile range . Works with all the factory equipment . No failures or problems .There are probably 5 or 6 different used configurations that I am aware of (or have done ) that work well too.But none are plug and play . It requires some knowledge and some customizing to work . The reason is we are using top quality batteries that are made for Ev’s , BMW , Chevy . KIA , Tesla , ETC.And adapting them to work . This gets an owner into lithium at a fraction of the cost .
If we were to go to a manufacturer like Gem did, we could get custom packs made for Gems . They would be perfect size , with specific brackets to mount them and all custom connectors so that they could only be hooked up one way . But instead of being $2500 new they would be $10,000 like what Gem charges . So a Gem owner would be better served to pay someone to install one of our new packs or one of the cheaper used systems others have used . All properly installed will work great for many years and would probably cost $600 - $1,000 for the install .
The only other option I know of would be to buy 6 drop in lithium 12v batteries and replace the ones you have . You would want minimum of an 80Ah battery . They are probably $800 Ea. For the ones that would work at 72v . (lots of them cannot be put 6 in a row) . This would be an easy drop in option .