In the current (2002) TSRGD 652 only has to be electrically lit if it needs to be seen by drivers who have just turned into that road within the last 50 m. Otherwise retroreflective is fine. (Schedule 17 is pretty difficult to follow on this!)
DfT have clearly stated that in the new Regs electrical lighting on all signs within a 20 mph speed limits will be optional, including ones that are safety critical like 616 (no entry). So if their latest draft of the 2015 TSRGD says something different, that is clearly an error that will hopefully be picked up in the imminent “technical review and general sense check”.
So I would only put forward for electrical lighting those 652s that are within 50 m on the start of a road (or a side turning at which you can join it in the relevant direction) and are unlikely to be within a 20 mph speed limit of either sort in the the near future. You might also wish to consider whether they are all actually needed or whether some can be removed completely.