Using the USB port as a reference, the size of the battery pack is roughly 71mm x 35mm, so it probably contains two 18650 cells side by side. Panasonic's best

Using the USB port as a reference, the size of the battery pack is roughly 71mm x 35mm, so it probably contains two 18650 cells side by side. Panasonic's best 18650s have a capacity of 3350mAh, which sets an upper bound of 6700mAh for the pack: http://na.industrial.panasonic.com/products/batteries/rechargeable-batteries/lithium-ion/series/cylindrical-series/CS474 http://na.industrial.panasonic.com/products/batteries/rechar... Those "5000mAh" 18650s you find on eBay come from Chinese manufacturers who stick random numbers on cylinders, so the actual capacity is probably off by a factor of 3-5: http://lygte-info.dk/review/batteries2012/UltraFire%20TR18650%205000mAh%20(Blue)%20UK.html http://lygte-info.dk/review/batteries2012/UltraFire%20TR1865...