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How can i get the low battery warning back on my MacBook?

I have a MacBook and I did not take care of the battery properly. It started to shut down unexpectedly at around 20% and then even at 30%. I got a new battery and it seems to work fine; it lets me get down to 6%. The only problem is that even with the new battery, a warning does not pop up telling me that it is time to plug in my computer. I was waiting for it to come up when my computer was at 6%, and instead it just died. I don't know if I need to change some kind of setting or what. Any ideas on how to fix this?

It is kind of funny that this debate still rages on. I’m going to give you the definitive way to keep your battery as healthy as possible:

Plug it in whenever you aren’t using it or whenever it needs to be plugged in. It doesn’t matter.

Leave it plugged in as long as you want, or leave it unplugged as long as you want. Again, it doesn't matter.

Lithium Ion batteries have no “memory effect” like older batteries, so they don’t require such meticulous care. Apple’s batteries are rated for 1000 cycles. And again, there is some debate about what constitutes a “cycle,” although (again) there should be no debate.

According to Apple, if you allow your battery to discharge to 50% and then charge it to 100%, and then you do the same thing tomorrow, you have used 1 cycle, not 2. So that means, if you plug it in when it still has 95% battery power and charge it back to 100%, you have used only 1/20th of a cycle. If you plug it in when you have 25% battery left and charge it to 100% you have used ¾ of a cycle, etc.

Here’s another fun fact: according to Apple, at some point soon after you’ve used those 1000 cycles it will still charge to 80% of capacity. So if you realistically get 5 hours of battery life before you have run through those 1000 hours, you will still get 4 hours of battery for a long time.

OK - so where does that leave us? Well, if you discharge your battery 100% every dayand charge it over night, you will get about 3 years out of the battery before performance drops to 80% — which still gives you respectable service. If you aren’t discharging your battery 100% and recharging it every 24 hours, then your battery will last a lot longer than 1000 days before you notice significant (20%) degradation in performance.

In other words, by the time you notice a significantly decreased battery life, you will probably be buying a newer computer. So plug it in whenever you want. Don’t worry about it at all. (And btw, you can leave the power plugged in as long as you want after the battery is fully charged. It won’t overcharge as long as you are using original Apple power adapters.)

So now you know the best way to keep a MacBook’s battery healthy and long-lasting: just use it and don’t worry about it.

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Try calibrating the battery. Follow the instructions at http://support.apple.com/kb/HT1490 , but before the battery gets into the sort of zone where it shuts down unexpectedly quit all of your applications (this should reduce the risk of a sudden power load causing it to quit unexpectedly during the calibration process itself).
Don't worry too much if it still shuts down without warning anyway at this point in the calibration, but follow the remainder of the steps outlined in the article (letting it rest for five hours without power after it sleeps or shuts down, and charging it up fully).
If the problem is still occurring after a full calibration try resetting the SMC (see http://support.apple.com/kb/HT3964 ), removing and replacing the battery, and try the calibration again.
You should aim to re-calibrate your battery every couple of months.

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I had reset SMC several times and changed my battery once. Unfortunately, my MacBook did not show low battery warning anymore. Then I found SlimBatteryMonitor, it works for me. You can customize the percentage of battery (if drops below x%) to show the warning panel too.

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