Rechargeable 4.2v / 3.7v 18650 Li-ion Batteries are slightly larger than AA batteries but they do look the same. They hold a much higher capacity than AA batteries and as such are usually much more expensive. However as we buy in Bulk, we can pass the savings on to you, so you can now buy 2 Rechargeable 18650 batteries for less than 8 euros and delivery is free once you spend €25 or more.  Why not buy the Performance 1200 Lumens Bike Cycling front light and 2 x 18650 batteries which all in will only cost less than €28 with free next day delivery.