Also, I would think that having the correct voltage is very import as they arent all the same. Its worth noting installing a battery holder with different specified voltage can permanently damage your equipment I would venture to guess.

Maybe I will propose and post this at Gearslutz likewise or someone else can start it if they like. To my knowledge the DX7 series, Matrix 6/1000, QS, Z1, Alpha Juno/MKS-50 and more all have soldered batteries.  

These are very popular instruments and would think there is interest in having this reference info.