Lots of us standardize our batteries (e.g., only use AAs), so that we don't have to play around with a million different types. However, you can't always get away with AAs for some devices. So, I'm curious, what do you make exceptions for?

First, why I standardize:

Pros:
1) Just charge your devices, throw 10 extra AAs in your pack, and you're easily covered for the weekend and then some.

2) You can buy/find them anywhere in the world. You can also pull them out of other devices (cannibalize 'em).

3) NiMH AAs work great. I have LaCrosse BC900 and a Maha C401FS chargers and I can recharge from solar, my car, a portable SLA battery, AC, etc. I use PowerEx 2700mAh batteries, which are the highest capacity available. I always have fresh trickle charged ones ready to go.

4) Non-rechargeable AAs are dirt cheap. The more expensive Lithium AAs work great in very cold temperatures. Alkalines and Lithiums (non-rechargeable) have incredibly long shelf lives.

5) Good flashlights no longer require CR123s.

6) My AA Gear:

• Flashlights: Photon Proton and Freedom Fusion, Fenix L2D premium, random others...
• Radios: Sangean DT200VX (AM/FM), Yaesu VX7/VX2 emergency backup power (ham), Uniden BCD396T (scanner)
• GPS: Garmin 60CSx
• Cell phone power-backup

And now, here are what I make exceptions for:

• Photon Freedom Micro lights (2xCR2016). I always have at least 2 of these with me, as they're on keychains and they're clipped to every bag I own. Very low self-discharge rate.
• Ham radio battery packs are proprietary Lion. (Yaesu VX-7 and VX-2. They have AA backups, but those are mainly for receive, not transmit.) Usually carry 2-3 battery packs per radio.
• Surefire E2E and some other random CR123 lights. I take a Xenon E2E camping, as IMHO the beam is better in fog than LED. But I don't buy anything new that requires CR123s. This is legacy equipment to me.
• Glo-toobs (A23): I just love these things. I keep them clipped to bags and I even EDC one.
• Radios for emergency use when on battery power (D cells): CCrane Radio Plus, Sony 2010, XM boombox, and too many others. (The Sony also requires AAs.) I also have C and D size "cases" for my rechargeable AAs, but I haven't used them.
• Green laser pointer (2xAAA). Useful for pointing out constellations when camping, as the beam is visible if there's no moon. (I use rechargeable AAA NiHMs.) This might be useful for emergency signaling, as it's so damn bright, but that's not why I bring it.
• Sealed lead acid (SLA) batteries, both portable and not so portable, that can be solar charged and power AC (120V) or DC (12V) devices.

So, who else is trying to standardize and what are you making exceptions for? Are the exceptions for critical items (e.g., water purification) or things you could manage without?

Fitz