Branch of wood push the flap and fill it. If you dont have te funnel cut the bottom of plastic bottle put it in and pass a branch through it thats the perfect method without propper funnel. I have done it multiple times.

Get a jerry can and someone to take you to gas station and fill up your car if it cant drive for 15-30minutes. The battery will most likely recharge enough in 15-30 minutes driving to start again after turning off.