A very useful guide - thank you. Original batteries are branded Lezyne, marked LIR123A Lithium Ion 3.6V 600 mAh - 2 Amp (Rechargeable). Equivalent battery code to LIR123A (rechargeable version of CR123A) is 16340. I found 700 mAh capacity cells freely available on eBay etc. Some vendors offer vastly inflated capacities (even 1500 mAh etc.) but I suspect these are fake.