I recently bought a Bell Spinfit bike speedometer for $16 at Kmart, a store near my house that I usually loathe for being out of the most common items. The AG12 1.5 volt battery out of the box had about a day's worth of power left so I tried a few stores for a replacement. Best Buy, famous for untrained and unknowledgeable sales people, didn't have it and urged me to go to CVS, which had some batteries that looked close, but did not exactly match the AG12 designation. I later discovered AG12 is a Chinese battery number. A guy at CircuitCity at least had good advice - try RadioShack. In my experience, the sales people at CircuitCity are superior to Best Buy's. I don't go to Besy Buy much anymore.
Being the persistent SOB that I am, I decided to go back to Kmart and get some satisfaction. After all, it sold me the defective battery. The speedometer was installed and working so I was reluctant to put more time in to return it. It's a nifty item and Kmart has for $1 less than Amazon. The Kmart store manager (Kim?) gave me $4 to buy a new battery, a fair settlement. So I strutted down to Radio Shack 400 feet away and the sales person instantly knew that an AG12 was an Energizer 386, the one I refrained from taking a chance on at CVS. I paid $5 for it. So a couple of gallons of gas and an hours later and a buck poorer, I was up and running. I usually use Radio Shack for niggling purchases like this, but maybe should try some big ticket items there, too.