45 minutes run-time is not ideal for a .5 acre. Especially if you have anything that will aid bogging down the electric motor (long/dense/wet grass). So that isn't comparable at all.
The Echo seems like it could do it, but again, we are now $200+ dollars more expensive than a gas one.
I am not a battery lawn equipment or anything hater, I even owned a plug-in hybrid for a while. However, the bigger the battery powered thing gets, the less financially attractive it becomes. The batteries are so dang expensive if one stops working after 5 years or just degrades that much, the entire mower is basically going to be junk. If the $180 battery breaks on a $329 mower, are you really just going to buy a new battery? Probably not, so it is a brand new $330+ mower every five years? Gas engines are so simplistic even abusing one and the mower will chug along for 15+ years easily without any maintenance.