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Mid 2009 Macbook Pro 15" Runs when plugged in but not on battery

edited July 2014 in MacBook Pro
I have a mid 2009 Macbook pro 15" that runs fine when plugged in, but not on the battery. When unplugged it will run for a period of time on a fully charged battery then shut down (immediately, not hibernating). If the machine is stressed on battery it will shut down immediately. I've replaced the battery, no change. The battery seems to be charging properly.

All this makes me suspect a voltage regulator, a loose connection on the board interface to the battery, or an intermittent short. Does anyone have any experience with this kind of problem?


  • Hi! Thanks for the post! Most battery issues end up being bad batteries, so the first thing to do is Google and download Coconut Battery, which will let you see the actual stats on the battery so you don't have to guess what's going in. If a battery charges but dies in a few minutes, it may technically be working but down to a very small percentage of its original capacity. Think of it like a 1-gallon gas tank -- when it's full the gauge will show you have a full tank, but you'll run out very quickly.

    Let me know what you see in Coconut Battery on both batteries. All to often a battery goes bad, then the user replaces it with a cheap 3rd party battery which is also bad, and then assumes the computer has a problem. It's not enough to assume that because the battery is new it must be a working battery -- it has to be a "known good" device, which means you have seen it working on another machine.

    If the numbers in Coconut Battery appear garbled or it does not seem to get a reading, that can point to hardware failure, but it's jumping the gun to assume this without looking at the numbers first.

    Thanks, and let me know what you find out!

  • Coconut Battery reports that the battery is "Good" and that the current charge is within a few percent of the maximum, which is slightly above the design capacity, and no failures are reported. I don't see anything that would suggest the battery is not in good condition.

    Running on the battery with the CPU loaded, the computer shut off suddenly (no hibernation) at about 28% capacity, as reported by Coconut. It dies much more quickly when the GPU is also loaded.

    Apple ran a 24 hour diagnostic on it and also concluded that the battery was okay, but reported that the logic board needed to be replaced. When I pressed them they said the problem was with "the sensors."
  • Weird. I don't know what "the sensors" means. I wouldn't put a lot of weight on an Apple diagnosis -- they really don't teach their employees much more than to run diagnostics, and they will very quickly resort to saying it's a "bad board" when they don't have an answer.

    Personally I am never 100% convinced a piece of hardware is good until I have ruled it out by replacing it and witnessing that the problem still occurs. It sounds unlikely that the battery is the problem, but you just don't know for sure until you've proven it beyond any doubt.

    A lot of bad unibody board will shut off like you mention under various conditions. This usually happens due to a faulty trace on the board that has grown weak due to ESD, or the expanding/contracting of the board, usually from heat. Often a trace will be connected when the board is cold, but then the board heats up, expands, and the trace will lose its connection -- sort of like a crack in a road that is not apparent when the road is level, but becomes apparent when one side of the road lifts up. When the trace disconnects it causes a short and the board powers off.

    There's not a lot that can be done in these cases. Sometimes it can happen due to static, so it's important to make sure the board is clean and free of dust. Corrosion due to liquid damage can cause it, and that should always be cleaned off with rubbing alcohol and a toothbrush. It's worth testing the RAM slots by powering on with one empty and then the other empty -- when a slot is not populated, the electronics related to that slot are not active, so I'd verify the problem still exists with one slot empty, and then the other. Sometimes you can bypass a problem by keeping a RAM slot empty.

    As far as repair, it gets very complicated very quickly, and being effective at it involves an expert knowledge of electronics, soldering, and also having the proper schematics (which are not easy to acquire, thanks to Apple). I would check out Ebay and search for "MacBook Pro logic board repair" until you find a listing relevant to your board. There are a lot of hacks out there, but there are also some good companies that might be able to repair it for substantially less than replacement.

    Thanks and good luck!


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