myo xp @ 18650 possible?

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I own an old myo xp
and i asked my self if it is possible to run it with 3,7V lithium ions if i only take 2 batterys and replace the 3rd by a circuit to get the voltage down to 4.5-5V

a 2. option would be to run 2 in parallel and then replace the 3rd with anything to get the 4.5-5V

any ideas how that could work?

i hope you know what i mean
dont have the best english skills :/
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now idea if that could work?

 

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is this that difficult?