This is a bit techno-geeky, but a lot of people have asked questions or expressed concern about the performance of rechargeable lithium-ion (li-ion) batteries, so I thought I'd write this up for anyone who's interested. There are a few things to know about these batteries that can help you get better performance out of them.
• What are li-ion batteries?
Rather than bore you with a discussion about chemistry, let me just point out where you commonly find these things. Pretty much all current smartphones, tablets, laptops and cameras, and a handful of new battery-powered flash units use li-ions.
• What are their advantages?
They pack a lot of power in a smaller, lighter package than older rechargeable battery technologies like Nickel Metal Hydride (NiMH), Nickel Cadmium (NiCd), and lead acid, they're widely recycled, and they pose less hazard to the environment. Also, unlike NiCd, they don't suffer memory effects that reduce battery capacity over time.
• What are their disadvantages?
Badly made or damaged ones can leak and explode, which is why airlines don't like them and also why you should always wait a minute or two before picking up a dropped smartphone. Also, they lose much of their charge within a month even if unused.
• So, what can I do to get better performance out of them?
First, a brand-new battery needs a few charge-discharge cycles to reach full capacity. Some folks get a new camera and then complain that they don't get as many shots out of the battery as they're supposed to. The key is to fully charge a new battery, use it until it's fully depleted, let it rest a few hours, and then fully charge it again. Repeat this cycle a few times, and the battery's capacity will gradually increase to it's specified level.
Second, li-ions like to be used and don't like to be fully depleted (after the initial conditioning) or left for long periods (weeks or months) with either a full charge or zero charge. Li-ions are happiest with a partial charge. This is why I fully charge them just before I'm going to need them, and when I'm done making photos, I'll store them with a partial charge until the next time I plan to use them. If you've got a laptop that mostly stays plugged in on your desktop, unplugging it once in a while to run on battery power is actually better for the battery than leaving it plugged in all the time.
Third, over time, the circuitry in the battery that tells your device how much charge is left can become inaccurate. The way to correct this is to fully discharge the battery, let it rest for several hours, and then recharge the battery. Apple recommends that owners do this once a month.
So, there you go. If you've got a new battery or an older battery that seems to be underperforming, a little care in charging and storing it might make all the difference.
[I'm not an authority on battery chemistry, just a photographer who relies on batteries a lot and has read a fair bit about them. The information I'm presenting here was gathered from manufacturers' recommendations and technical articles. If you'd like a fuller technical explanation, there's an excellent one here.]