Lithium ion batteries work best if they're kept topped up. I'm surprised Apple recommends draining once a month.

Completely draining and topping up a LiIon battery will kill it much more rapidly than keeping it topped up.

LiIon will also naturally degrade over time. I think for 90%+ of all lithium batteries (polymer or ion) the battery life will fall off extremely rapidly after 2 years regardless of how you treat it. That said, I still have a handful of batteries that are 5 years old and still work great (for my long-since-discontinued Sony IP55e MicroMV camcorder)

at work we have a few users who never take their laptops anywhere - they're constantly plugged in. Nothing kills batteries faster.

Silly question, but the commentary on whether you should run down the battery now and then is interesting. What's the opinion here?

Def a good idea to completely cycle your battery every now and then (i.e. use till your laptop totally runs out of juice and then totally charge again).

Battery chemistries have improved since the old NiCad days, but they will still exhibit some memory.

Also, batteries tend to have a lot of smarts in them nowadays - cycling the battery will let the electronics have a better idea of when the battery is actually full or empty. This will result in a better charge when you use the battery for real.

Afaik, that last point is why Apple recommend power cycling your battery every now and then.

"Battery chemistries have improved since the old NiCad days, but they will still exhibit some memory."

This is incorrect. Lithium ion batteries do not exhibit memory. However, the digital tools to check them can develop a memory, which leads to inaccuracies. (and is why it is recommended to occasionally cycle the battery). Cycling is hard on lithium ion, so you should try not do to it too often.

> This is incorrect. Lithium ion batteries do not exhibit memory.

I said chemistries - NiMH still exhibit a memory.

> However, the digital tools to check them can develop a memory

I think I mentioned that.

You never want to fully discharge a lithium ion battery. As I understand it, most batteries consist of multiple internal cells, and fully discharging the cells increases the chances that one of the cells will reverse polarity and ruin the battery.

Lithium ion batteries contain safety circuits that will attempt to shut down the battery before it fully discharges, but of course batteries continue to naturally self-discharge even when they are not being used, so such a shut-down battery could still fully discharge over time. So if you discharge a lithium battery to the point where it stops working, it is not actually fully discharged, but you want to recharge it soon, while it still holds this residual charge.

This is why all new lithium ion batteries ship partially charged and recommend a full charge before initial use.

I think apple say somewhere that the perfect battery use is that of a commuter, use the battery for an hour or two each morning, then charge for the rest of the day.

Sadly I've been almost 100% on power, and my 2 year old macbook pro now has a battery life of about 30 minutes. Apparently its at 22% health, hopefully that can be reversed a little.

I think jwilliams summed it up nicely, but here's a site to read all about batteries on. http://www.batteryuniversity.com/

i always keep my laptop plugged in when home and in use - otherwise it just sits on the table not plugged in and not on