Caution when charging LiPo batteries:
Many headlamps use Li-Po (Lithium Polymer) batteries, the same ones in an iPhone etc.
These are the flat rectangular packs, used in many lights including Ay-up. The ones that have cylindrical batteries are Li-ion.
Recently, a friend was charging his LiPo battery from Batteryspace with their approved charger overnight when the smoke detector went off. He ran downstairs to find it on fire! Luckily nobody was hurt, but there was some damage to the house and several nearby batteries. This was the battery many folks got with the Night Lightning kits years ago.
I had a dental colleague who found his very expensive Loupe light battery pack on fire in his lab.
I read of a case where an Ay-up pack caught fire as well.
These are rare, and apparently happen if the battery is punctured, shorted or overcharged by a malfunctioning charger.
I believe Li-ion packs can also burn, but these are rarer. They are used in laptop computers as well as bike lights. I build battery packs with protection circuits that should not overcharge, but I suppose anything is possible.
If you're bored:
http://batteryuniversity.com/learn/article/safety_...
Standard instructions for charging these lights always say "do not charge unattended, charge on non-flamable surface such as concrete."
Many folks with high power LiPo for radio controlled drones and cars use a special LiPo-save charging bag:
http://www.amazon.com/Battery-Fireproof-Storage-Ma...
My advice for anyone charging LiPo and Li-ion batteries for headlamps:
Charge and store them in a metal cookie tin, or preferably a special LiPo-safe charging bag. Ideally placed in a metal sink, tile or concrete floor or granite countertop when charging. Don't have them charging when you leave the house.
I have bought 10 bags for folks with Bentblasters. I'll bring them to races etc.