Get a Sullivan Hi Torq. It is smaller than the Hobbico and can draw up to 25 amperes. It spins a 91 four stroke like it was a 1/2 A two cycle. I use a 24 ampere hour rated battery. Used to use a lawn mower battery.

I had a Hobbico 90 starter and it was just down right anemic, probably dirty brushes or something. Got the Sully and never looked back.

Cheers,

Chip