My husband uses a Gel cell battery for his ECV. Best is to check the medical supply Co you more then likely will purchase from and make sure they supply you with the FAA approved battery.
My husband used to take his EVC to the side of the plane and then as he could hang onto the walls of the plane and the seat backs-- he could get to his seat via that method. No longer able to get to weat with out the use of an isle chair Husband uses airport transport for wheelchair service to the plane door.
I always disconnect the battery cables. Maks sure your EVC is actually off -- no via the auto off method. Place EVC in neutral or the auto brakes will wear them selves out while in flight. The EVCs are strapped down. Some times our EVC gets it's own inflight storage container. Most of the Airport ground crew is aware of the special needs for the EVC. Make sure you have an extra Key just incase.
We have my husbands EVC meet him at the arrival gate. then he can get around the airport unassisted.
Most ECV's are sold with gel batteries now. Very few are sold otherwise.
I fly with mine now the last 4 years. I ride it to the plane door and take the key with me. I also take things like baskets and arm rests off before I get to the airport and put them in their own bag that I take on the plane with me. The airline does not count this bag as part of my carry on allowance, it is considered medical equipment.
I don't disconnect the battery cables or anything else. As long as I have the key the only way that this can be operated is to put it into neutral and pushed.