The chair suddenly lost power and now the lights flash continuously. The chair won't take a charge. A repairman tried fixing it at a local shop and said he put a new battery in and it sizzled. Now he is vacation for 2 weeks and I am without a chair.

If he put in the batteries (2) properly, they should never sizzle. Some will emit a very minute spark when the final connection is made, but that is normal. There are fuses coming off of each battery to the power controller that will blow at 40 to 100 amps or so, depending on the chair; these will blow before the chair frying, or the circuit breaker will trip, or the controller will fry and all will be quiet on the chair, so I am going to say that the batteries weren't properly hooked up, otherwise on of the above items would have shut everything down. Continuous flashes indicate trying to start the chair while it is still on the charger, or with the joystick off-center. Make sure it is unplugged and notohing is resting against the joystick. If it's still a no-go, then you have either a joystick issue or controller issue. You will need to test those by replacing with known good controller/joystick, which a dealer should be able to do for you. Good luck.