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Will batter life decrease if I constantly leave my macbook plugged in 80%-90% of the time?

That's probably the worst thing you could do for your battery.

You should use the battery frequently, draining it anywhere between 25%-75%. You should do a full discharge/recharge once a month.

If you're not going to use the battery for an extended period of time (e.g. >1 month), you should drain the battery to 40% and store it in a cool dry place.

Bottom line: Don't leave your MB constantly plugged in and remember to use your battery. If you do the above steps, you'll probably get about 3 years out of it.
 
If you are leaving your laptop plugged in for extended periods of time, it's sometimes best to remove the battery. Also, in general, it is healthy to fully charge and discharge your laptop battery every so often, i.e. do not keep it in a fully charged or discharged state for long periods of time. What you are describing should not harm your battery life too much though, but it still is not good for it.

You can also monitor your battery's health and stats via Coconut Battery.
 
If you are leaving your laptop plugged in for extended periods of time, it's sometimes best to remove the battery. Also, in general, it is healthy to fully charge and discharge your laptop battery every so often, i.e. do not keep it in a fully charged or discharged state for long periods of time. What you are describing should not harm your battery life too much though, but it still is not good for it.

You can also monitor your battery's health and stats via Coconut Battery.

Whatever you do, don't run your MB straight on AC! It slows down your processor and increases the risk of your motherboard getting burned out. Apple advises this way..
Also, you should be fine plugging in for 80-90% of the time.. as long as it's not 100%! Make sure you use your MB on battery a couple of times a week, and do the calibration once a month, to keep the battery running correctly.
This is straight form Apple... :D

http://support.apple.com/kb/HT2788
http://support.apple.com/kb/HT1490
 
Whatever you do, don't run your MB straight on AC! It slows down your processor and increases the risk of your motherboard getting burned out. Apple advises this way..
Also, you should be fine plugging in for 80-90% of the time.. as long as it's not 100%! Make sure you use your MB on battery a couple of times a week, and do the calibration once a month, to keep the battery running correctly.
This is straight form Apple... :D

http://support.apple.com/kb/HT2788
http://support.apple.com/kb/HT1490

Running the MB on AC slows down the cpu and burns the logic board out ???
 
Sorry guys, I can't find a documented source for the logic board issue, but it has come up in the forum before if I can recall correctly.
 
that will kill your battery pretty darn fast so i wouldn,t do that if i were you i would unplug it and discharge it fully at least once a week:apple:

Standard Maintenance
For proper maintenance of a lithium-based battery, it’s important to keep the electrons in it moving occasionally. Apple does not recommend leaving your portable plugged in all the time. An ideal use would be a commuter who uses her MacBook Pro on the train, then plugs it in at the office to charge. This keeps the battery juices flowing. If on the other hand, you use a desktop computer at work, and save a notebook for infrequent travel, Apple recommends charging and discharging its battery at least once per month. Need a reminder? Add an event to your desktop’s iCal.

http://www.apple.com/batteries/notebooks.html

How much clearer can Apple be? DON'T be plugged in 100% of the time, but DON'T do full discharge more often than once a month.
 
Its easier by just using the laptop as a laptop. I've gone through over 23 charge cycles in 2 weeks so far. I just use it. Probably the only time I plug it in is when I'm at my desk or the battery is under 20%.
 
Its easier by just using the laptop as a laptop. I've gone through over 23 charge cycles in 2 weeks so far. I just use it. Probably the only time I plug it in is when I'm at my desk or the battery is under 20%.

LOL.. nobody is MAKING anybody use their laptop in any specific way. The OP was asking for the best ways to maximize battery life and I'm just posting straight from Apple's website. Not something I made up or anything..
 
My advice: don't worry about it. The computer is smart enough to manage it's own battery. Plug it in when you can, use it on battery when you cant.
I've been using my MacBook this way for over a year and a half. iStat Pro shows 100% health, and i still get about 3.5 hours of internet usage on one charge, with wi-fi and bluetooth ON.
 
Keeping the computer plugged in won't kill ur battery, my old MB went from 100% health to 99% health in a year, it was plugged in all the time. New batteries do not get charged while plugged in when it is fully charged.
 
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