I hooked up the 400 amp Curtis controller I bought off Ebay to four of the gel cell batteries.
It took a little bit of work to do, because I had to drill out some of the cable terminals to fit the posts of the batteries and motor, to hook it all up.
Then, once I hooked it all up, I realized I had it wrong and had to re-wire it!
I pulled the twist throttle off the motorcycle and hooked it up to the two connector pins on the controller.
Check out the controller-bench-test spin-up.
I also picked up a big smart charger which has a "gel" setting on it. It also has a "desulfate" feature which might be good to have with this batch of batteries.
The first battery I tried charging had the lowest voltage on it. The charger ran the "desulfate" feature and then blinked, indicating it didn't work so well.
Then I ran the charger on the next battery, with a better voltage, and it worked great, charging the battery very quickly. Another neat feature on the charger is that it tells your battery state-of charge too!
I will run the charger on the other batteries and see which ones pass muster.