Macbook Pro shutting down abruptly at 30% battery left – under HEAVY load only

Anybody else have this problem? I tried to google-fu this one and people seem to say that it’s a battery calibration issue – as in the OS and battery getting out of sync, but I don’t think that’s the case here. As long as I’m not beating on the thing – just light load web surfing or whatever – it’s fine and it’ll run down to less than 5% with the proper low battery warning and all that. My issue only happens under HEAVY load. As in browsing through high-res digital photos beating on the processor, disk, and RAM a lot. No warning, no nothing, just *flick* craps out around 30%. Light load casual use it runs fine down to under 5%.

To be fair I do have 400+ cycle count on the battery and it does say only "Fair" for battery condition, but it still did this even in the 200/300 cycle count range and good or excellent or whatever the heck the best battery health rating is. Before I thought it was from heavy current draw from Firewire external drives or something, but I moved my recent stuff to the local internal HD and still have the same issue, so it’s not external drives or anything.

Anyways, just wondering if anybody else has experienced this or not?

overheating? My desktop did that under heavy load and it was because the processors were getting too hot since the cooling system leaked and was empty.

Could be, but I manually crank the fans up via smcFanControl when I’m beating on it, so I doubt that’s the case. It only ever happens at around 30% battery remaining too. If it was thermal shutdown it could happen whenever.

I think what’s happening is a cell or two in the battery might have either had or developed higher than normal resistance, which then causes a higher than normal voltage drop under load. Enough that the whole system will take a poop.

Technically I’m out of warranty, but I think I might take it to the Apple Store and tell them what’s happening, and see if I can get a free battery out of it. Have heard of them giving those to people out of warranty. Right now battery is in the teens, but since I’m not really beating on it it’s still running. Don’t want to buy a new battery since this one still has plenty of life too.

Does this ever happen when it’s plugged in? If not, it’s probably the battery can’t provide the power demanded and the system panics and shuts down.

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