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Comment by OJFord | Hacker News Reader

Mac. Does sleep when battery flat, rather than "die" completely - but how long do you trust it for? Knowing Sod's Law, I opted for the run.

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When battery gets low enough, a sleeping MacBook [Pro] will actually wake up from sleep and hibernate to disk all by itself.

(terminology: 'sleep' is suspend to RAM, requires battery to keep active. 'hibernate' is suspend to disk, no battery required after RAM copied to HD—obviously requires enough HD space to run the persistence.)

Wondering if that is Pro specific, or applies of Air too.

It applies to Airs too. All customisable through pmset - https://developer.apple.com/library/mac/documentation/Darwin...

Newer Macs will save the memory to nonvolatile storage so they can withstand total power loss. The question of trustworthiness remains, though.

Not only that, but they do it when the lid is first closed. That way, if it dies in an hour due to a low battery... oh well. (This is also why the more memory you have, the longer it may take for the laptop to go to sleep after closing the lid.)

My experience with my Macbook is that around 20% battery, it just dies. No sleep, no hibernate, it just goes completely dark and when I plug it back in it has to boot from scratch.

Sounds like you have a bad battery or something like that, which is causing the battery meter to be inaccurate and is thus interfering with the rest of the process. To safely sleep/hibernate your machine the system has to have a pretty good idea of just how much energy is left in the battery, since it has to initiate the process before the battery goes completely flat. On a properly working machine, you should get all the way down to 0%, and then it will forcibly sleep if you don't do it yourself.

Have you tried an SMC reset? That's the low-level whatnot that controls the battery, and sometimes it can get confused.

I tried an SMC reset today, and it changed nothing. It still just dies right around 20%. (At least, I think I reset the SMC. There wasn't any obvious feedback confirming that I had done so.)

Yeah, the SMC reset procedure is pretty opaque. Sounds like you're probably at the point of needing a repair. Hope you're in warranty, although given how these things go I imagine you're probably not.

Nah, I've had it a few years, so it's out of warranty. I'll probably have to replace the battery eventually. I don't mind if the battery's capacity is decreasing, I just want it to auto-sleep before the battery dies. Maybe there's a way to set the auto-sleep threshold to 25% or something?

Yea, I've never had issues like that, and I've used Mac's exclusively for since they came out with the unibody.

That's definitely a battery problem. I had the same issue after a few years, got the battery replaced and now it works as you'd expect. Of course, the batteries aren't cheap, so it depends on how annoying you find it :) I lived with it for about a year.

It's definitely a hardware issue. I owned two Macbooks and both went to sleep/hibernate when battery reached 0%.

My MBP doesn't die even at 3%, it just goes to the "hibernate" state.

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