Lightmalls – Ultrafire 501b XM-L2 5 mode 18650 for 9.25usd. Cheap, solid, great driver with >2 amps HI and about 1 amp on MED so medium is usefully bright and gives about 2.5 hours, while HI is very bright. Much more trail friendly than my older XML-T6 which gave only 0.6 amps on MED. I’m on my 4th gen of 501bs (at the price it is worth a yearly upgrade) and while the T6 were good, these are great.
Like all the Chinese lights I have used these need to be tightened up, and you need to wrap cells in tape to keep them snug – I also use 1 or 2 x 2.5mm magnets as spacers, as the cells I have are from old laptops so are ‘unprotected’. This means they are 2.5mm shorter than protected cells. Cells need to be v snug as a sharp knock may move them which will interrupt the current… which is how the mode change works on clicky-clicky.