One of the decisions people tend not to make about the stuff that goes into their 72 hour kits is about the batteries. Some people are optomizers and will get the best flashlight, the best GPS the best radio and and the best batteries. But they all use different sized batteries.
If you are looking at a disaster one of the times you don't know is how long it will last and what will be the most important. For any particular disaster or emergency only about 20% of your stuff will be really important for that disaster. But we don't know beforehand which 20% that is. If you're helping out in a search and rescue it might be the GPS and 2-way radio, if its a blackout the flashlight and radio receiver.
The best thing to do is to have your powered equipment share all the same kind of batteries, that way you can just carry a lot of batteries and use then for which ever equipment you need. If they all use AA cells then you can carry a lot fo them and use them however you need.
You can even get external battery packs for your cell phone that let you pull in AA batteries.
AA cells are the most versitile sizes out there and you can get them just about anywhere. Supermarkets, convenience stores, office stores, dollar stores, truck stops all have them. Exotic batteries like 123A or watch batteries not so much.
While I like my big 3 D cell LED Maglite because it multitasks as a club. It also works really well useing AA to D cell adaptors. They are just plastic holders the size of a D cell with a spot in the middle for a AA. It doesn't last as long as a D cell but that is a tradeoff I have decided to go with.
