High-side switch to disconnect battery
I'm not sure what the issue is with using a MOSFET as follows:







simulate this circuit &ndash; Schematic created using CircuitLab

I drew in the body-diode of the MOSFET separately just to remind that it is always there.
The only thing you need to do to drive this circuit is ensure that the Gate-Source voltage on the MOSFET is higher than the Vgs threshold voltage of the MOSFET  you choose. If that's the problem you are referring to then you need a gate-driver IC with built in boost-voltage/charge-pump. Most of these will be classified under "high-side mosfet driver" - like the MIC5021 datasheet  (just the first one that popped up doing a search, not particularly endorsing that one). 

The downside to this solution being that you have to conduct into the load through D2, which will cause a small voltage drop and will need to be size to handle the current the load will require. 

M2 can be quite small compared to M1 since it is only handling small signals.