S8 Elite II CPAP.com Battery Question

I just purchased a ResMed S8 Elite II, and am looking at battery power options for long airline flights. The one on CPAP.com looks like a pretty nice package - Lithium so it's lighter and smaller:

https://www.cpap.com/cpap-machine/cpap- ... cable.html

My question is the battery included is 12V 6.6 Amp Hours. From the ResMed guide, I need at least 11 Amp Hours for 8cm treatment for 8 hours (no humidifier):

http://www.resmed.com/us/assets/documen ... -guide.pdf

I think 8cm is pretty low, considering some of the values people here have posted. The lowest value ResMed has listed (6cm) is still 11 Amp Hours.

So I just wanted to know if I'm missing something - the reviews on CPAP.com seem pretty positive, and multiple comments on it lasting through the night.

I've done a lot of searches on batteries on this site, but couldn't really find an answer.

Thanks,

BM

TheOneBlackMage wrote:I just purchased a ResMed S8 Elite II, and am looking at battery power options for long airline flights. The one on CPAP.com looks like a pretty nice package - Lithium so it's lighter and smaller:

https://www.cpap.com/cpap-machine/cpap- ... cable.html

My question is the battery included is 12V 6.6 Amp Hours. From the ResMed guide, I need at least 11 Amp Hours for 8cm treatment for 8 hours (no humidifier):

http://www.resmed.com/us/assets/documen ... -guide.pdf

I think 8cm is pretty low, considering some of the values people here have posted. The lowest value ResMed has listed (6cm) is still 11 Amp Hours.

So I just wanted to know if I'm missing something - the reviews on CPAP.com seem pretty positive, and multiple comments on it lasting through the night.

I've done a lot of searches on batteries on this site, but couldn't really find an answer.

Thanks,

BM

The listing you mention (11 amp hours needed for 6 or 8cm, 8 hours) is when you are using an inverter. An inverter converts the DC power into AC power so you have standard house power. An inverter wastes a lot of that battery power.

The Resmed Converter (not Inverter) basically just regulates the DC power from the battery so it has no possibility of damaging the machine. It is much more efficient than an inverter. Down at the end of that battery document on page 15 is a chart for use with the Resmed Converter. It says 8 amp hours is needed for an 8 hour night at 8cm when using the Converter on your S8 Elite II. That's closer to your goal.

Thanks for finding that - I missed the converter vs inverter difference. It does say in the document that the converter is more efficient.

So for the Elite at 8cm it says it draws 0.70 Amps per hour. So 8 hours = 5.6 Amp Hours. So the battery on CPAP.com being 6.6 Amp Hours would be enough. The ResMed document adds a 50% safety margin, bringing it to 8.4, rounded to 8, but I'm pretty sure you can drain lithium batteries down pretty far without damaging them, so this battery would be fine.

Thanks!

TheOneBlackMage wrote:Thanks for finding that - I missed the converter vs inverter difference. It does say in the document that the converter is more efficient.

So for the Elite at 8cm it says it draws 0.70 Amps per hour. So 8 hours = 5.6 Amp Hours. So the battery on CPAP.com being 6.6 Amp Hours would be enough. The ResMed document adds a 50% safety margin, bringing it to 8.4, rounded to 8, but I'm pretty sure you can drain lithium batteries down pretty far without damaging them, so this battery would be fine.

Thanks!

I don't know the characteristics of Lithium Ion batteries but my personal experience makes me believe they lose their amp hour capacity slowly over time (think cell phone or laptop). So I'm saying a new one would probably work but what about when the battery is a year old? There's just not much room to play with there. I noticed the 50% safety margin too but didn't mention it because especially with a Lithium Ion I wouldn't want to take that margin away.

Edit: I googled the characteristics and my suspicions are correct. Some performance loss is noticeable after a year. And they only last 2-3 years whether you use them or not. Sounds like my cell phone experiences.

an alternative for flying is to get a seat with a power point and an adaptor and plug it in, this may involve paying more than basic economy, also you often need to apply to airline well in advance to get their approval for your brand and type of CPAP, forget any humidifiers, of course

nomoore wrote:An inverter wastes a lot of that battery power.

<sigh> Here we go again...

Modern inverters are ~90%+ efficient so they do not waste "a lot of that battery power".

Cheers,

Bill (IEEE)

TheOneBlackMage wrote:So for the Elite at 8cm it says it draws 0.70 Amps per hour. So 8 hours = 5.6 Amp Hours.

If your specific need is for operation in a commercial aircraft cabin, you need to take altitude adjustment into account. For operation in a pressurised aircraft cabin (equivalent to ~2400m altitude), you need to add energy consumption equivalent to an extra 3 to 4cms H20 additional at sea level.

Cheers,

Bill