The Nitecore F2 Charger: 46.5 grams plus battery weight, eg two X 18650s at 48 grams each = 6800 Mah of charging for a weight penalty of 142.5 grams (not bad), but if you add a second pair of batteries (96 grams) you have 13600 Mah for 238.5 grams which is just about unbeatable. The best bit is you can even use smaller, lighter lithium batteries for a shorter trip: http://charger.nitecore.com/CHARGER/F/F2/ The batteries can be recharged with a USB cable even from a solar charger on the trail.
The Nitecore F1 charger is even better weighing only 30 grams. Add one 18650battery for 3400Mah at 47.6 grams (Total 77.6 grams) or as many more as you need, so this little guy plus four batteries equals 220.4 grams for 13600 Mah!. You can’t beat that. Or you can add an even lighter battery if your needs are small: http://charger.nitecore.com/CHARGER/F/F1/ I bought one of these for under A$10 on eBay!
You will notice that the device will charge other battery sizes. The 14500 battery for example is identical in size to a AA and the 10440 is identical in size to the AAA. Some/many torches made for this size battery will take a lithium 3 volt battery though they will heat up a lot on full beam – and may burn out the LED. You will need to check this against the torch you own.
When storing (lithium) or any batteries in your pack you should keep them together with a rubber band and place them in a ziplock bag to prevent their touching/discharging – there is very little if any risk of fire from 18650 batteries as they have internal circuit protection against such risks.