I've had good luck with Panasonic (tho in general I don't like Panasonic stuff). My last system was a 4 line for pots, replaced by the now year old similar system for voip. The batteries on newer panasonics are just aaa sized and easily replaceable.

Nothing completes with Engenius range, tho. Before the retirement of my pots lines, I also had one of these, the range was nearly 1 mile.