 Wondering why your battery's dead even though you haven't been using it? Even when left completely disconnected, all batteries will slowly lose their charge over time, and certain battery chemistries will self-discharge faster than others. While they're great for frequent use, some nickel metal hydride batteries can lose 30% of their capacity per month just sitting around. That's why it's best not to use those in your smoke detector or emergency flashlights. Stick to alkalines there. Lithium polymer and lithium ion are much better at retaining charge, but can still lose several percent monthly. On a side note, most rechargeable lithium polymer batteries will ship with only 50% charge for safety. Just top them up for a few hours upon arrival. In the end, your best bet for battery longevity is still alkaline, with an average shelf life of five years. Hard to beat the classics.