I forgot about your dislike for proprietary batteries. The BK has a AA battery pack available, but I think that is an option that will add to the already high cost for a professional grade radio. (It may be an included accesory.)
The Unication G4/G5 pager has a Lithium-Ion battery pack, that is charged via a micro USB, or an optional desktop charger. I don't know if there is a AA option. Battery life is reported to be up to 24 hours with a "quiet" system, and 14-16 hours with busier systems, in the FAQ page for the pagers.
Spare proprietary battery packs are available for the SDS, and probably for the G4/G5. If you're car camping, the USB charging cable for either can be plugged into the cigarette lighter or DC power outlet in your vehicle to keep the pack charged, at least when the radio isn't being listened to. These won't be any heavier than carrying extra AA batteries.
I know you don't like proprietary packs, but if you really want to be able to listen to MCSO, if it is that important, you may need to reconsider. But it's your choice.
John
Peoria