Resmed S9 optimal battery runtime configuration questions

[Crimson Nape]

I have a Resmed S9 and the 90 watt 12-24 volt DC power supply. I understand that there is rarely a 1:1 trade off, thus my questions.  My questions are in 2 parts. Ultimately, I'm looking at the most effective configuration.
Part 1 - If I use two 12 volt batteries of the same size which would be the most advantageous wiring method, in series. in parallel, or no difference?

Part 2 - What would be a better configuration; two 12 volt "X" amp hour batteries wired in series to produce 24 volts, or one 12 volt at double (X*2) the amp hour ranting of the 2 smaller ones.

[Gary1of2]

Ifvi am getting you question right. I know for instance when we have a 24 volt scissor lift we get longer battery life using 4 -6 volt deepcycle batteries wired in series for24 volts. I think the same applies to your question.

[Crimson Nape]

Thanks!  I think srlevine1 answered my question in another thread (Referenced Thread).  There is some energy loss whenever you change it.  I'll experience less loss if I input 24V into the power supply as opposed to inputting 12V and letting it convert it to 24V.

[OMyMyOHellYes]

There is not enough energy loss with ResMed's 12-24 V DC converter to worry about. I had a friend once that referred to a syndrome called PII (Preoccupation with Inconsequential Increments). I think this falls under that category.

If ResMed was not of a mind to force their customers into buying their converter to make the unit run, I would say sure, go with 24 V direct. But since you can't go 24 direct, then just use 12 and don't worry about it. Without heated humogrification, the S-9 on the converter is really energy efficient anyway. I can safely get 8 nights out of a 35 AH battery on it.

OMMOHY

[Crimson Nape]

A big Thank You for that information.  I didn't know what the conversion loss would be.

Red