Needed a replacement ‘AG13′ battery for my cheapo Halfords bike computer. Happened to be picking up some items in B&Q – saw a button that looked the same called LR44 , could not recall the AG13 code, but dammit they look the same so I bought a 2-pack on spec.. (£2.98). Got home realised they were not same code… growl. Went into Kingston to buy food… looked for battery in several places but could not find one anywhere. Eventually dragged myself into Maplin… no luck, the assistant (looks up on computer and) said “discontinued”. Resign self to buying new device…  

Drop in on a small independent electrical retailer on walk back and ask again.  Man says “Oh yes, you want  a ‘357′ . Same thing new code. Sell them all the time”  Deal! (£2.50 for one)  Get home. Look up code on Google…. Arghhhhhh… THEY ARE ALL THE F’ing SAME!  Yes, AG13 = A76 = LR44 = 357 

Feel like a wally for not checking before I buy (can get a 10 pack on t’internet for under £7) and feel crushed by complexity again. 

How come the world agrees on ‘AA’ & ‘AAA’ (for example)  but not on these button types?