I keep one of the gigantic Costco packs of alkaline AA's for one specific emergency use. As a backup power source for my Yaesu FT-60R HAM transceiver.

Normally, this radio is powered from it's OEM battery pack (NiMH technology - this radio is an old design and does not use LiION).

First line backup power is Eneloop AA's in it's optional accessory battery holder. Note: The instruction manual specifically says not to use NiMH's in the optional accessory battery holder. However, what they are warning against is not to put the NiMH's in that holder and then use the Yaesu charger to charge them. It is fine to charge the individual NiMH's in a separate charger (like my Nitecore or Maha mentioned above) and then put those charged batteries in the accessory battery holder. My guess is that the Yaesu charger is a crappy one, containing no protection circuitry to prevent overcharging, overheating, etc. They depend on the OEM battery pack to provide those features. But the accessory battery holder loaded with your own NiMH's would not provide those features. Thus the warning not to use that setup with the Yaesu charger. It would have been better for the instruction manual to say "Do not charge NiMH's in the Yaesu accessory battery holder", but instead they said "Do not use..." I guess you'd call that "Out of an abundance of caution...". Disclaimer: I did not ask Yaesu about this, I am speaking from my Electrical Engineering background. There is no reason that their OEM NiMH battery pack would be different than their accessory battery holder loaded with your NiMH batteries - save for protection circuitry that they may have included in their OEM pack.

Second line backup power for the radio is that Costco package of Alkaline AA's. There's got to be 40 or more batteries in that package (typical for a Costco item!) I would not leave those alkaline batteries in the radio. They are only a last resort emergency backup to power the radio should all other sources of power be exhausted. I also still have a few AA sized LED lights that could use those batteries as a last resort emergency backup as well.