catymag, you are not correct here. First of all, no info inside a nuvi is kept alive by the battery except contents of the RAM (which doesn't contain the internal filesystem, obviously).
And second, the flash chip is logically divided into so called regions by unit software. There is one region for non-vol memory, one for the internal filesystem, one for fw_all.bin, and so on.
So technically NVM and internal filesystem are of the same kind.