Surefire sells
spare battery carriers and
batteries at a reasonable price.
I have been buying my batteries from
botac . They have great prices (20 batteries for $20 US). While some people do not like botach, i have never had any problems with them in the years I have been buying stuff from them.
My battery carrier is a
witz case. I carry an assortment of batteries in there. Mine holds 7 AA, 4 AAA, and 4 123A. They are separated by cotton pads to avoid contacts touching, eliminate rattling and gives me extra tinder. It is waterproof and can hold a good supply of whatever configuration you want. I will probably change my mix to just mostly 123A's and a few AAA's as those are my most commonly used outdoors.
I also carried the AA's because that is what my wife and kids were using. But now that I got my wife a Surefire, we can change the mix before our next camping trip next week.