Can't comment on a brush cutter but both my father and I have been mightily impressed with the little Husky battery chainsaw.
He's has his for quite a few years now, I've had mine about a year. They sit on the shelf for a while then get heavy use. For a sense of runtime (with a brand new chain straight from the shop) I felled and logged into 1ft sections a 25ft ash tree and all its branches on a single charge of the battery.
Its so nice being more or less quiet, also not having to faff with fuel and trying to get the damn thing started is really nice. Switches on instantly and away you go. Very rarely use the "normal" mode as it's usually on eco. Dull chains knacker the battery though.
Not been fault free, Dad had some corrosion on the battery terminals just out of warranty but the dealer honoured it and had them fixed free of charge. Since then we keep them in dry sheds, his was in a slightly damper environment to begin with.
Wouldn't be without it now, there is the time and place for bigger saws but for non continuous use its a definite contender in my opinion.
I fancy a battery chainsaw - you can sneak into the forestry and nobody would ever know
Of course before Tony Blair and the Forestry commission ruined it you could forage in the forestry anyway with a cheap licence - ah well it was a right that had only been in place for 800 years