Rechargeable lithium-based technology currently provides the best performance for your iPod. You can also find this standard battery technology in devices such as mobile phones and PDAs. Like other rechargeable batteries, these batteries may eventually require replacement.
Lithium-ion batteries pack in a higher power density than nickel-based batteries. This gives you a longer battery life in a lighter package, as lithium is the lightest metal. You can also recharge a lithium-ion battery whenever convenient, without the full charge or discharge cycle necessary to keep nickel-based batteries at peak performance. (Over time, crystals build up in nickel-based batteries and prevent you from charging them completely, necessitating an inconvenient full discharge).
Most lithium-ion batteries use a fast charge to charge your device to 80 per cent battery capacity, and then they will switch to trickle charging. This equates to roughly two hours charge time to power an iPod to 80 per cent capacity, then another two hours to fully charge the iPod (as long as you are not using the iPod while charging). You can charge all lithium-ion batteries a large but finite number of times, as defined by the charge cycle.
Using and recharging 100 per cent of battery capacity equals one full charge cycle. A charge cycle means using all of the battery’s power, but that doesn’t necessarily mean a single charge. For instance, you could listen to your iPod for a few hours one day, using half its power, and then recharge it fully.