Is it good to let the battery run completely down?

You should plug in whenever possible and [*Calibrate your Battery*|http://docs.info.apple.com/article.html?path=Mac/10.5/en/9036.html] every month or two. -GDF

There are two primary things that impact the life of your battery... The number of recharge cycles and age. Age is pretty much self explanatory... after about 3 years, Lithium Ion/Polymer batteries start to lose capacity (regardless of the number of cycles on them). So far as actual cycles go... a new battery should generally hold a full charge for up to about 300 cycles. After that, it will gradually lose it's capacity (but it should still be very usable for quite some time). One full cycle is considered to be from a full charge to completely discharged. However, partial charges only count as partial cycles. For example, if your battery is at 90% and you charge it up to 100%, that is a 10% difference and only counts as 1/10th of a cycle. You would have to do this 10 times for it to equal a full cycle. Likewise, if you let your battery go down to 50% and then fully charged it back to 100%... that would be a half cycle... so doing this twice would result in a full cycle. So, as you can see, the less you discharge and recharge, the fewer cycles you will have which will result in prolonging your battery life. As mentioned, it is a good idea to follow the battery calibration procedure every month or two if you primarily use your MacBook on AC.

I agree all the way to the point of the calibration. You only need to calibrate if the battery indicator seems to be reporting the wrong information. lithium ion/polymer batteries can be damaged if you discharge all the way. I only calibrate mine when I have to, no more.

Glor

Glorfindeal wrote:
I agree all the way to the point of the calibration. You only need to calibrate if the battery indicator seems to be reporting the wrong information. lithium ion/polymer batteries can be damaged if you discharge all the way. I only calibrate mine when I have to, no more.

Glor

Glorfindeal... I agree completely. I actually don't remember the last time I calibrated my battery. I'm just usually a little reserved when it comes to recommending something different from what Apple says:

*Calibrate the battery in your MacBook or MacBook Pro every month or two to keep your battery functioning at its fullest capacity.*

Typically you need to really really really discharge a Li Ion/Poly battery to damage it. You basically need to let it run down until your machine won't start... and then leave it unused for a few months to let the charge drop even lower. The circuitry in the battery is specifically designed to not permit a recharge if it drops below that super-low point.

Regardless... I do the same thing... Unless I'm having a problem, I don't calibrate it. If I plan on being in a situation where I'll be using my MacBook on battery quite a bit... I'll usually let it run down just to make sure it has good battery life (as I don't do this often because it's almost always plugged in).