MacBook Pro Won't Sleep on Reserve Battery Power

Hello fellow mac-users and mac-geeks,

My Macbook Pro 2007 (2.2 GHz, Santa Rosa) was recently repaired by apple. The logic board was replaced due to the Nvidia issue. (If you don't know what that is, take a look in Apple's support documents.)

I then bought a non-apple replacement battery from http://famous-battery.com and installed it in my laptop.

Now, when my laptop is on reserve battery power, it will give me the warning message, but it won't go to sleep when the battery runs down. Instead, it will force itself to shut down as if it immediately lost power. It seems like the equivalent of holding down the power button to force a shut down.

The machine will not automatically safe-sleep, let alone sleep normally.

Any ideas?

Thanks.