21700 and 26650 Li-Ions

Over the past decade the 18650 format has dominated lithium-ion battery chemistry, and it's still the sweet-spot in terms of compatibility, availability and value. However the demand for greater energy reserves in a single cell has led to the development of new formats.

While the 18650 cell seems to have peaked at about 3,500mAh, new-generation Li-Ions such as the 26650 and 21700 are appearing with capacities of 5,000mAh and more. More mAh does not make a torch any brighter, but does make it run longer on a charge.

However these cells are physically bigger (the first two digits give the diameter and the third and fourth digits give the length in millimetres before a protection circuit and outer wrapper are added) so they don't fit into torches or chargers that aren't designed for them – although the opposite is NOT true, 18650 batteries can usually fit into a torch or charger that is designed for a new-gen battery.

There's still a good case to be made for buying two 18650s rather than one of the bigger batteries – having two cells means you can charge one while using the other and/or carry the spare for those priceless moments when you realise you forgot to charge your battery after your last outing!

Click on the pictures below to see details, photos and prices and drop me a line to discuss discounts.