Electronic – High capacity – EEPROM chip

You can get code that is known to work, but it will not be guaranteed to work on your particular hardware configuration. You will need to configure the code and maybe even modify it.

A couple of years ago, I wrote a simple LCD library. At the time, I used PIC18F4450, but I have also tried this code on PIC16F887. It should work with many chips, as long as you know what you do. To make things easy for you, it also has an example main.c file.

Yes, an EEPROM is a type of nonvolatile memory which can hold data even without any power for a significant amount of time (the actual time depends on temperature and other conditions).

There are a few other non volatile solutions for you to consider:

1) Internal Flash memory - Most microcontrollers nowdays have Flash for code storage and some provide it for user data and logging as well. This also has limited write cycles and requires block erase before changing bits from '1' to '0' (you store data elsewhere in the meantime and then rewrite it).

2) Internal FRAM memory - TI has devices with FRAM memory which is nonvolatile, can be accessed very simply (like any other memory location. Reads are also destructive as writes (though in your case this might not matter since the number of cycles is 10^13 or so at 85 degrees celsius).

3) External Flash memory - You can add memory externally to hold a few megabits of data rather inexpensively.

Depending on the rate at which you want to save (and whether you can shutdown nicely) you might be able to increase the effective number of cycles available for you.