Just for FYI Not sure if it's been covered before but I found out the hard way after chewing my Sony metal tape that using an Energiser brand AA battery jams the tape head from coming all the way down onto the tape. This is because the cap on the + of the battery is higher than Duracell AA batteries which work fine
Interesting, have you mic'd it to see the size difference? Energizers are a little cheaper and go on sale alot but I prefer Duracells.
Just to say: I've given-up on buying disposable batteries... and gone with Ray-o-vac rechargeables, and a Duracell charger--saving tons!