Gassner AA LR6 AM3 Alkaline Batteries

[reflowman]

30 months ago I bought a load of wireless Thermostatic Radiator Valves (MAX EQ3).
They came with two Gassner AA LR6 AM3 Alkaline Batteries each.
I'd never heard of them and, as the valves are cranking "quite a bit" and the receiver is active all day long, I guessed the batteries would be dead in a year tops.
But no. They've all kept going well past 2 years.
I've no current consumption figures, but either Max know a thing or two about low power machinery or Gassner Battery Co. (Shenzhen) Ltd make very good batteries.
Any experience of Gassner out there?