Which Radiator Valve to buy?

I have my own gas boiler fitted. The flow to each radiator is governed by auto-balancing valve bodies with TRV attached - you set the valve body to the correct manufacturer-depicted setting required to get 20c difference in temperature between flow and return pipes (based on radiator kW output rating), then the radiator will always get the correct flow to maintain optimum heat transfer.

The TRVs are then just on/off valves.

Ok, that makes sense, but still a bit hard on the batteries though.