As for the battery. I have one 200x battery and a few older less capacity ones for my Husqvarna devices. The 200 fits the devices. I may be wrong but isn't the 300 one wider as in it would stick out to one side?
I tried the gasoline and battery 540 top handles at the Paul Bunyan show last year and with the chains on them as delivered and the performance was extremely similar with the battery one easier to stall out.
I'm not sure of the width of the two batteries, comparatively. I'm pretty sure the two batteries that fit this series saw are different than the original batteries and will require a different charger (QC500.)
I can usually get a full day's work off two batteries, unless bucking lots of firewood or the chain loses some sharpness.
The two biggest drawbacks to these saws are the tendency to stall out (and stop) whereas a gas saw may stall but continue to power through a cut.
The other BIG drawback is the clutch cover outlet is tiny and often clogs. When bucking or stumping, ill often have to clear the channel out multiple times with my finger. If noodles are coming out, it clogs even quicker than chips.
Currently, I'm still having issues with my break sensor. Hopefully today I will be splitting the saw and investigating between loose or faulty sensor. WHY a saw with a physical/manual chain break also needs an electronic break sensor is BEYOND me, but that's what the geniuses at Husqy decided upon.