I told him to look into ditching the SLA batteries and upgrading the controller if possible. I don't know if getting more power out of the motor those things come with is possible
Definitely go with a lithium pack. If the motor is brushed, it can likely take 1/3rd more voltage without any significant increase in the wear-rate of the brushes [due to arc-ing]. If it is 36V, go to 48V...if it is 48V, go to 60V / 72V. Controllers get somewhat pricey-er above 72V. If the motor is brushless, you have many more options.
As far as the amps go, add a temp sensor and a motor-fan...and slowly raise the amps until its still below 93C / 200F as a temporary peak of less than five seconds [during acceleration].
IIRC he was saying the thing has something like 600 lbs of SLA's, just replacing those should make the vehicle tackle hills a bit better, say if the weight of the pack was maybe 200 lbs? Plus getting some more juice flowing through the motor, I think he'd be a lot more enthused about using it-was somewhat disappointed after paying a fair amount for the vehicle, finding out it's well...........a Zap.
Another friend of mine bought a Zebra back when they came out. Didn't see him for a while and then asked him how he liked it, he said he sold it saying it was a dangerous POS with a really crappy range.
Yuba Mundo w/BBSHD
Specialized Hard Rock w/9c clone, statoraid, hubsink
Trek Fuel 90 w/BBSHD
Above all run on 14s4p 52v li-ion
Ecobike folder 36v
Currie Flyer scooter 24v on 24ah of SLA
Every trip made with electric bike is one less car trip, saves money, no toxic fumes, less noise, less impact on roads.