With the drills I've found it useful to have 2 smaller batteries just to reduce the load on my wrists. Mine are all Makita, 3 brushless drill drivers, a reciprocating saw and have 2x3A, a 4A and a 5A batteries.

I have used a 36V Stihl Chainsaw at the tree loppers yard and I have to say it was most impressive. The key with chainsaws is a sharp chain.