lulz buying 1 battery at a time  is the most expensive way.
		
		
	 
Yeah not really sure where one would buy those in bulk.  There's Ali express but I don't know if I'd trust that.   I think once Tesla builds their gigafactory they will drop in price and become more available.
I want to retro fit battery operated stuff to use them actually.  Rechargeable AA's and such are too low of a voltage compared to their replacements and have a very high self discharge rate, so they often don't work in lot of things nor are they idea to keep in storage for emergency.   But a single lithium ion cell has a higher voltage (maybe a tad too high) and a longer shelf life where they stay charged longer, so one cell can replace two AA batteries.  May need a voltage regulator or something though.  Maybe even just a dropper diode.