Thanks for the helpful reply, it helps clarify the need.
As for dissipating excess current, the idea I had in mind was that the pass element would only dissipate current to the extent it was demanded from the load. For example, if the battery were 16.8V and the threshold were 14.0V and the load were drawing 1 microamp, the intended thermal waste would be 16.8-14.0=2.8*1uA = 2.8 microwatts. If the load current exceeds the capability of any component in the supply chain, that would be "left to the reader" (=not concerned about that eventuality at this stage.)
From my prior (limited) experience with linear/LDO regulators, I've not found one that has pass behavior below it's minimum input voltage (for example, a 7805 linear regulator works when the supply voltage is 8 volts (and the current is within limits), but I don't believe it has a specified behavior below some lower limit (example, 4 volts may just result in the regulator being an open circuit between source and load.) If there is a part that you (or anyone reading) is aware of that would help towards my objective, I'd like to know!
As for partially charging the battery - it's a nice idea I hadn't thought of, however, I'm constrained to work with commercial charger where the cut-off point is pre-determined.
Another constraint I left off my initial posting - all voltages would be >0 (that is, no negative voltages, and no condition where the pass element would need to deal with negative voltage when the threshold is positive.)
And yes, switch mode device would be a more general solution, however, I need to preclude that option.
As for a series element controlled by an op-amp, that was somewhat the direction I was headed, but I was hoping that there would be a name or more concise description for this sort of circuit function.
So, thanks for helping me think through this!
Dave