My apologies if this isn't the correct place for this question. I am not familiar enough with some of these concepts to move forward on this without bouncing the ideas off of some more experienced people.
I have this CPAP (medical device for sleeping): https://mytranscend.com/wp-content/uploads/2018/09/103347-rev-l.pdf
They sell a battery for this that costs more than I'd prefer to pay, and can only be used for operating this CPAP. I was hoping to gain some versatility and save some money with a non-proprietary battery for this. This is all on pg. 34 of the above link. The AC adapter for the CPAP is rated for an output of 18 VDC, 1.67 Amp, and the batteries are rated for an output of 14.4 VDC; at least this is how I interpret the manual. Can I power this CPAP with something like this: https://www.amazon.com/Poweradd-Pilot-Pro2-Notebooks-Smartphones/dp/B015OAJFOC/ref=pd_sbs_107_2?_encoding=UTF8&pd_rd_i=B015OAJFOC&pd_rd_r=SZEFWNV0SN48T70QDKDZ&pd_rd_w=Q7LzD&pd_rd_wg=vYYR3&psc=1&refRID=SZEFWNV0SN48T70QDKDZ? I don't think this battery has the right connector, but I thought I could create an inline adapter that will connect one of the existing battery connectors to the connector type on my CPAP. My DC barrel connector has (roughly) a 6 mm outer diameter, a 4.33 mm inner diameter, is roughly 9.9 mm long, and has a pin on the inside of the cylinder that I can't reach to measure with my calipers. After a little bit of research, I think it might be an EIAJ-05 connector.
With my lack of knowledge in this area, here are some of the questions that I could use some help with addressing:
With a power cord that outputs 18 VDC, 1.67 A, and a battery that outputs 14.4 VDC, will one of the native settings on this battery (5V/9V/12V/16V/19V/20V) power this CPAP if I can create a working inline adapter?
If none of the native settings are a good idea, can I add power diodes to my inline adapter to drop the voltage down to an acceptable amount?
Provided I can find the correct connector for my CPAP, are there any flaws in the plan to build a small inline adapter to connect one of the existing battery connectors to my CPAP's connector?
Am I overlooking anything with this idea as a result of my inexperience and lack of knowledge?