ok, ive looked into this issue and have seen many threads (including here on MacRumors). almost all responses point to a battery issue. I have a 2011 Macbook Pro8,2 @ 2.3Ghz. About 2 months ago it started powering off randomly. as if you removed all power sources from it. As of recently the occurrence has become more common. my first thought was the battery as i had the original one that had about 360 cycles and 85% health at 5200mAh. i purchased a new battery from iFixit and installed and reset the SMC. the issue did not go away. it happened within 20 min of new battery install. the issue DOES NOT happen with the power cable attached. which, after installing a new battery and resetting SMC makes me think the logic board may have an issue. any thoughts?