I see there are all kinds of options and types of batteries. I would like to purchase a rechargeable battery pack and charger for my Fenix TK60 instead of buying D cells over and over. What type of battery (Li-ion, etc) should I be looking at? Also, what about maH? There are so many options I don't want to go the wrong route and not be able to use the light to its full ability or worse damage the light. Thanks.