how to recover file after battery exhaustion

Unless there was an auto-saved backup copy (MS Word and a few other apps do this), then the files are lost, since they were only in RAM and never saved to disk.

In the future, you might want to use SmartSleep, which can automatically set the system to hibernate so you can plug it back in, turn it on, and have all your files back like you did before.

Also, make sure the system is going to sleep when the battery is about to die rather than just dying while it's awake. If it just dies, then it could mean you have a battery problem.

The system is supposed to warn you when your battery is getting low, and then will put itself to sleep when the battery gets dangerously low. Are you saying that Snow Leopard is no longer doing this? If so, you may want to try [resetting the SMC|http://macosx.com/forums/howto-faqs/302002-reset-system-management-controll er-smc.html].

Note that, on any system, sleep uses a small trickle of battery power. If you don't plug the machine in quickly enough (a few hours at least is safe, in my experience), it can drain the battery completely and you lose any unsaved changes unrecoverably. I'm not sure how things work with hibernation - I would hope that the system is smart enough to hibernate when there is still enough battery power left to write out the RAM to disk, but I don't really know, as I hate hibernation and never use it.

I think you are seriously confused about terminology, as your post doesn't make a lot of sense. Rebooting refers to the act of restarting the Mac, just as if you turned off the machine and then turned it back on again. It restarts the system from scratch (ie, with a "fresh desktop").

Sleep is a completely different thing. It allows the machine to stay on while cutting power to as many components as possible. This allows the machine to look like it's turned off, but it retains its state and wakes up with all the same apps/windows open.

If you are putting your machine to sleep and finding later that it has not retained the state, as you seem to be saying, that means the battery has died and the machine shut down. Not a nice, gentle shut down, like when you choose Apple -> Shut Down, but an abrupt, kick-in-the-head sort of shut down that has the potential to do damage to your system software. Not to mention that you'll lose unsaved changes to open documents. This is a problem, and you need to address it.

Hi Thomas

Are you saying your MBP is sleeping at low battery?

My 2008 MBP 15" stopped doing this after a clean Leopard install: it warns you that it will sleep and then powers off abruptly, all unsaved changes lost. Connecting the power adapter allows you to start it up from cold.

Battery status is OK in Energy Saver, have reset PMU, recalibrated battery.

Everything is fine apart from the missing ability to sleep. Other people seem to be reporting a similar issue =0)

Are you saying your MBP is sleeping at low battery?

Honestly, I don't know, as I haven't gotten into that situation since installing SL. I'm intentionally trying to do it now... been using the machine with wifi on and screen brightness at max for 1.5 hours and still plenty of charge left, but I'll post my results when I run out.

However, note that the post you're replying to was not about acknowledging or refuting such a sleep problem. It was about clarifying terminology and establishing a base of knowledge from which to continue the conversation. As a former tech support person, when I hear someone say that they rebooted "with all my opened windows" instead of with a "fresh desktop," that indicates that there's a serious disconnect between what is going on and the terms being used to describe it. Support via this kind of forum is only as good as the clarity of the communication... after all, I can't see what he's describing.

I'm pretty sure "rebooting with open windows" refers to the recovery from the memory state which was saved to disk (hibernation). Leopard would do this on laptops (which is why the sleep light would be solid for several seconds while it wrote the memory to disk), but it sounds like Snow Leopard turns this hibernation feature off by default.

Basically what it does (or did) is this: if the battery power completely dies (or the battery is removed) during sleep, the next time the computer is rebooted it will show a different progress bar while it brings back the saved memory state from the hard disk, then all windows and even unsaved documents will be back.

the next time the computer is rebooted it will show a different progress bar while it brings back the saved memory state from the hard disk, then all windows and even unsaved documents will be back.

I'm aware of what hibernation is, as I mentioned it in my first reply on this post. But to say it once again, it is an error to use the word "reboot" to refer to waking a machine from either sleep or hibernation. I think my reasons for making this clarification have been adequately stated.

Hi Thomas

I was just curious as to how widespread this sleep at low battery issue was. It's becoming apparent that it affects some but not all Macbooks.

I'm the IT guru at my company and to be honest I'm so used to translating user-speak into technical-speak I don't even know I'm doing it - it's almost subconscious now =0)

I was just curious as to how widespread this sleep at low battery issue was.

I don't really know... probably nobody does. Reading here will not give you a good indication, as you don't find many people saying "Hi, just letting people know I'm not having the low-battery sleep issue." The best indication would probably come from someone who manages a large number of Macs for a company or school. Back in the 90s, I had to manage over 50 Macs for a department at a large university, and saw a pretty good cross-section of the types of problems people had with Macs at that time. However, I suspect that such environments will not have converted entirely over to SL yet, and may not for some time.

Okay, I finally ran out of battery power. The machine went to sleep, I plugged it back in and woke it up... all is good. No shutdown due to power loss. No different from how it has ever behaved.