Question about Black & Decker Stc1820cm

One battery lasts about 30 minutes. We have 2 of them and when we mow all the edges, including around the bushes and trees (about 1 hour), the two batteries are just enough.
I can highly recommend the device as a whole.

I can't say exactly. So far (approx. 2 years in operation), it has never run out. But I only use it for the edges. About 10-15 minutes of operation per use (at level 2). The battery is always plugged in when I store it.