Re: Meters with displays? I remember them!
The corresponding "smart" meter is bigger still - they say they only have one model, which presumably has to be able to cope with the gas consumption of a large factory rather than just a pensioner's bungalow.
Exclusively designed for residential and SOHO customers. But if you imagine how big a ten year design life battery needs to be (even if it doesn't last) you'll understand. You're looking at around 10 Ah capacity, 3V, sealed unit and a very conservative cell design to support the intended design life and potential use in temperature ranges +45C to -25C.