This light is a bit unusual in that it requires three 18650 batteries while most headlamps use only two. It will work on any 18650 battery but if you are really interested in a long run time between recharges, try NCR/Panasonic 3400 mAh batteries. Here in the USA they cost about $6 each on eBay. I tested a pair of the NCR batteries in a bike headlight that uses two 18650 batteries. It ran between 2.5 and 3.5 hours using the cheap $2.50-$3 Trustfire/Ultrafire batteries rated at a fictional 5800/4000 mAh but 16.5 hours (in flashing mode) with the NCR/Panasonic batteries. Shipping Li-ion batteries internationally these days seems to be a big problem so you may want to find sources for them within Ireland.