A wheelchair from ebay

Last week, I won an ebay auction for an electric wheelchair. Its a Twister Junior electric wheelchair in need of TLC. I got it for £62.

That will provide the motors, the gears, the wheels, the chassis and the batteries. The motor controllers are using a "DX BUS" protocole that nobody knows. I have other ideas to control the motors, so that's ok.
Motors are veryu quiet, but use a lot of power. my 3amps PID controllers from a previous project will not cope with that, so I need to find another way.
Also, the motors work on 24v. I would prefer to use 12v as power source. I will have to investigate and see if 12v make the motion fast enought. so far, I just took it in pieces and cleaned it.