Comment 13 for bug 811777

First, I still think there is a good argument for percentage as a useful statistic because your time remaining is a function of what you're using your computer for (gaming/video editing/flash vs word processing), while the percentage is not. Granted, users are going to make very rough estimates, but eh. As I said in my prior post, I think that both statistics are more useful when you can access both of them.

From what I've gathered, the most important factor in maintaining battery health is temperature. High temperature = bad. Kind of hard to fix in software though.

This table summarizes a bunch of does and don'ts. Almost all laptop batteries these days are Lithium Ion batteries. http://batteryuniversity.com/learn/article/do_and_dont_battery_table

When you store a battery, it unavoidably loses some capacity (not charge--capacity, ie, your battery used to store 1000 mAh, now only stores 800 mAh overall effect is that your 100% charged battery doesn't last as long). You can reduce this effect by storing batteries at about 40% discharge (ie, charge to 100%, discharge to 40%, store). This table compares battery storage at 100% and at 40%: http://batteryuniversity.com/learn/article/how_to_store_batteries
Also here is a nice picture illustrating capacity loss: http://batteryuniversity.com/learn/article/capacity_loss

Old batteries like Nickle Cadnium had a "memory effect" where the battery would "forget" how much capacity it actually had unless you fully dischared it and then fully recharged it. Lithium Ion batteries DO NOT have this behavior, and it is generally better for the battery to AVOID a full discharge. This is because repeated partial discharges of the battery increase the total number of charge cycles. Practically speaking this means you want to start charging the battery when it's at 20-30% instead of at zero. This page has a table summarizing the result: http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

The references I've used here are from batteryuniviersity.com because their site has nice sections and I can link you to specific things. Here are some more sources that give good overviews of how to maximize battery life:
http://www.mpoweruk.com/life.htm (this goes into some of the chemistry of batteries)
http://forum.notebookreview.com/hardware-components-aftermarket-upgrades/91846-notebook-battery-guide.html#post1696318 (A good practical guide, though he recommends monthly full discharges to calibrate the battery which is not good practice with lithium ion batteries)
http://en.wikipedia.org/wiki/Lithium-ion_battery#Prolonging_battery_pack_life (of course Wikipedia has something to say)

I hope this is helpful. Have a nice day.