The internal EEROM on a PIC is probably not a good place to store data. One, the space is very small, two, the EEROM has a wearout lifetime.

Have a look at 'serial memory' of the 24LC512 variety. These are simple to interface but are only a small size for a logger. The M25P64 and M25P128 are much bigger but a little harder to use. Probably the best solution for data logging is the SD/MMC cards which are outstanding size for the money.

HTH
Brian