The point has been well made and is now taken for granted that all our electronic devices should share a common battery size, with AAs being the most referenced. The argument is typically "I can take the batteries from my GPS and use them in my headlamp," or "My spares can be used in either device," or "AA batteries are available everywhere."
How often does having a common battery type actually get played out with these arguments? Has anyone ever taken the batteries from their headlamp and placed them in their GPS? Or conversely, do members here fly in the face of the common battery wisdom, and use a mix of two our more cell sizes (like me)?
For all except the thru-hikers, I suspect the need for a common battery type is a myth, and like the "need" for heavy packs and 12" waffle-stompers, reality is far from need. I believe it's a myth because:
--We're usually knowledgeable enough about the use of our devices so we know what our battery needs will be, and pack accordingly. Often a set of batteries will last far longer than a typical 2-5 day adventure, and we know which device needs spares and which don't.
--Some electronic devices can be satisfied with lightweight backups or modified behaviors when batteries die: map and compass, asleep before darkness, Photon on necklace, etc.
--Devices that use AA batteries are typically bigger and heavier: a Steripen using CR123A vs. one that uses AAs, headlamps, flashlights, GPS, etc. By seeking lighter items (AA vs. CR123A vs. AAA), we wind up with asymmetrical battery types anyway. I know half of us will race out and buy the first AAA-powered Steripen if it's ever produced.
There's also financial motivation: money spent leveling the battery-type field could be put to better use, as many electronic devices are $50+, and that could be used for a lighter quilt, or tarp, etc. We happily drag our AA GPS, AAA headlamp, and CR123A Steripen into the woods, since we'd rather use that money elsewhere in our kit.
I have an 1X AA headlamp, a 2X AA GPS*, a 2X CR123A Steripen, and a 1X AAA flashlight (for trail markers). Three different battery types! Each does it's job very well, or is fairly new, or would cost a lot to upgrade. Each device has been tested in my "lab" and in the field for battery life, so I have a pretty good idea how long I can go before replacement. For 2 night trips, I don't carry any spares, but it's comfortable knowing that I can last 5 days if necessary.
So how many different battery types are you toting around?
*Lately, I've been using my phone in a waterproof case. Cell phone batteries are a lot cheaper than a new GPS, and I have to carry my phone anyway. But I guess the phone batteries are just another battery type to carry!