I have had a Bosch Rotak cordless mower for 5 years now, at that time, it cost about £325. No problems, and still going. The battery lasts long enough to cut front lawn and rear lawn, twice, without recharging, I would estimate the combined lawn size at 170square Metres. I also have Bosch Cordless hedge trimers, again, after about four years, no complaints.
One point... I would suggest, if you plan to have a range of cordless garden tools (eg mower, trimmer, hedge trimmer, etc), to consider that if you choose from single brand, you may be able to "share" the charger (and, possibly battery), and, hence, save you from filling your shed/garage with chargers!