I'm trying to standardize too. I was trying to do it with 18650s and 16340s. My thought was that with a decent supply of rechargeables, and some solar power, there would be no need to fall back to scavenging AAs. My issue with 1.5V fuel is that my preferred lights get so big with 2x AA in series. But I can't find a solid, small FM, MW, SW radio that uses Li-ion. So I still have to keep AAs around... So much for the standardization.
My issue with such rechargeables is that they take too long to charge up. Even with a good power supply for a charger. But solar?.... Several long days of rain and depleted batteries could have you trying to conserve your candles for a working light source.