As others have suggested, it's very simple to make a little 'O' ring for your battery w/ anything at hand. Wire, balled up tinfoil, pinched up paper or cardboard, a washer, etc. It need not be exact, just good enough to keep the battery from shifting.
When you get back home, save yourself a LOT of future grief by buying one of those cheap multi meters that accurately measure voltage. I bought mine eons ago for $5 and it has taken care of all the guess work. Now I know exactly what the voltage is of any battery at any time, an invaluable thing. Sometimes even new batteries are flat, so you need to know that if it occurs. Also, some cameras are real fussy about voltage, while others work fine w/ "close enough". For now, sunny 16.