Dallas do a series of 8051 derivatives that have external RAM encapsulated, this is used to keep the program memory and external data memory. The management for teh battery is on chip.

The one I have is DS5000FP (it's actually a SIM), there are more recent versions which are in IC form.

(They are used by banking industry etc who need secure storage. By using RAM instead of FLASH the chip is able to wipe it's own brains in an instant the moment any tampering come into play. So they are marketed as being secure against physical attack.)

Anyhow, these give you battery backed storage with no need to write any extra code.

Daniel