I'm having this issue for about a year now:

When I run my macbook pros Battery down, there comes the low battery warning. After a while the system just goes down without suspending anything to my harddisk. When I restart my computer it does a normal start and after logging in I'm experiencing a lot messages due to the reset time. I correct my system-time and restart my mac and the system is back to normal.

Usually I'd say: Replace your CMOS-Battery (I know I have an EFI-Firmware), but where is it?. Or in other words: Is there a "System"-Battery, that would prevent my mac from forgetting the time?

Since I'm not running down my battery to 0 very often I only experience this issue from time to time and never took time to do anything about it.

iStats battery-Status says: Health:83%, Cycles:333, charge 50%...

Update

The Apple Forum helped me out with this. I had not heard of a SMC, which can be reset. (System Managment Controller). I reset my SMC and now the computer has gone back to normal.

Procedure:

1. Power down mac

2. Press shift+ctrl+alt+power button

3. Release all and Power up normaly. (my loading-led was indicating something had been done.)

Thanks a lot!

I'm still not sure, if the models with internal battery pack have another EFI-battery at all.