The SPD-601000A controller (24-60V 700-1000W) would work however we do not recommend using it with a 36 Volt 7Ah battery pack because it can draw more than 14 Amps from the battery pack which I will explain more about below.
The original 7Ah batteries can output up to 14 Amps continuously. At 24 Volts 14 Amps is 336 Watts so the original battery pack is a good match to the original 24 Volt 250 Watt motor.
If a third 7Ah battery was added to the battery pack then it would be a 36 Volt battery pack with a 14 Amp continuous output rating, so it could handle powering the original 24 Volt 250 Watt motor overvolted to 36 Volts, or a 36 Volt 500 Watt motor and controller.
We do not recommend mixing old and new batteries, batteries with different Ah ratings, or different brands of batteries together into a battery pack. The reason for this is that the batteries in a pack need to have the exact same charge and discharge curves so their Voltages do not become unbalance during charging and use. If the Voltage of batteries in a pack become unbalanced then the unbalance will get worse each time the battery pack is used until some of the batteries are overcharged and others are undercharged, which will eventually damage the batteries and cause them to fail. Mixing different batteries together will work for experimental and design proving use however do not expect for them to last very long if this is done.
With a 36 Volt 7Ah battery pack we recommend using a 36 Volt 500 Watt controller. Any of the 36 Volt 500 Watt controllers for brushed motors on our 36 Volt controllers page would work equally well for the job.
A 36 Volt 1.6 Amp charger such as our CHR-36V1.6A3P would work with the Razor Dune Buggy and also with the 36 Volt 7Ah battery pack.
For a motor upgrade choose a motor without a mounting base because most motors with mounting bases will not fit between the Razor Dune Buggy frame tubes. The motor can be attached to the frame with threaded rods. For a 36 volt system MOT-36500X2500, MOT-36750, and MOT-361000 are popular choices.
We also have several Razor Dune Buggy Modification Kits available.
What would my list need to be for going 36V.
I've looked around but I figured I'd take in some more input if anyone has anything new. I'm looking to add one more stock battery, a 36V speed controller, 36v charger.
I was looking at using 24-60V 700-1000W Electric Scooter/Bicycle Speed Controller with Throttle, but I am unsure as to the wiring going from the dune buggy throttle to the controller.
A motor upgrade would be next, and I am open to any suggestions on that as well.