I purchased the Extended Range Plus Pack from @LithiumGods and installed it back in April. Installed it in my 2012 E6 which had 6 Polaris Gels in it. The install was a complete piece of cake as the packs dropped into the existing battery tray with zero modification. I used the existing threaded rod and wingnut setups that were holding the old batteries down to secure the new packs to the metal battery tray so just had to drill two holes. Mike was in my area on travel and dropped the battery packs off, reprogrammed the controller and charger, and gave me some quick instructions. About 45 mins later I had the cart back up and running on lithium power.
The difference was noticeable immediately more power, quicker acceleration, and no trouble coming up the hill my house sits on. My previous range on the gels was 12 - 15 miles if I let it get down to nothing. I put 32 miles on the Gem this weekend and the lithium pack was just under 50% drained. It would be challenging to get to the true bottom on the pack. The factory drain calculation on the battery gauge on the dash has to be adjusted to at least be closer to accurate otherwise it will show empty long before you need to plug in. I did not pick up much in the way of top end speed (maybe 1-2mph now runs 33 - 34mph when fully charged) but that is most likely related to the gear ratio currently in the GEM.
If you are on the fence about making the transition to lithium, I highly recommend it. If not, and you need a set of 6 Polaris GEL Batteries, send me a message. Located in Lakeland, FL.
Also, how much was the conversion?