Transcend battery questions

I need help from someone who has a Transcend CPAP with the P8 or P4 battery and a voltmeter. I would like to know the voltage when the battery is fully charged and the voltage after a night of use. Can anyone help me with this please?

More info:
I am planning a hiking trip in late November and need a lightweight CPAP solution for 3 nights. I have researched quite a bit and bought a Transcend 3 Auto miniCPAP along with the Transcend DC Mobile Power Adapter. According to this document (pg 44) the input voltage to the DC Mobile Power Adapter can be 10v - 15.5v DC. I intended to build or buy a custom battery pack and add a voltage regulator to keep the voltage within that range. So I would need a custom battery pack, a voltage regulator with low voltage cutoff, and the DC Mobile Power Adapter to power the CPAP.

Then I noticed in the doc listed above that the Transcend battery output is 14.4v DC. That sounds a lot like the nominal voltage of a standard 4S (4cells in series) Lithium Ion battery pack. So I'm wondering what electronics are included in the Transcend pack. If the output of the pack varies from 16.4v down to about 12v then it is not regulated and I should be able to get away with just a 4S battery pack and low voltage cutoff and do away with the voltage regulator and the Mobile Power Adapter, thus saving weight and money. I have a nice hobby charger that can charge whatever battery pack I come up with.

I've also thought of just buying the P4 battery and opening it up and using the electronics with a larger battery pack but that would be an expensive option I think.

Thanks!
Nicholas

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