Replacing DX7 and DX7II cart batteries?

[amv]

I have RAM carts for both the DX7 and the DX7II, and I can't seem to find any information on replacing their batteries. Unlike the synth itself, the carts don't appear designed with this in mind; the plastic shell seems to split beneath the label decal, suggesting it's not meant to be separated, and unlike the D-50, there's no slide-off hatch to access the battery compartment.

Also, I know the DX7 ROM cart doesn't have a battery, but I swear I once read that for some reason, the DX7II ROM (not RAM) does. It doesn't make sense, but is this true? I usually prefer using ROM carts for their lack of battery drama, but is there some weird design quirk in the DX7II ROM that makes a battery necessary?

Thanks!