but I'd like to be 100% sure that 7.2 V or 7.4 V works perfectly without any risk
What Phase is going to tell you is why risk an $18,000 digital back over a $70 battery?
What I and others have told you is we are using the $20 7.4 volt batteries without issue -- and the exact same battery is now spec'd at 7.2 volts now anyway, and I measured their output with a voltmeter and they are within 0.
04 volt (NOT 0.4 volt) of the Phase battery. Doesn't mean we won't have future problems though, so your money and your choice
Best,