Lithium battery for CPAP machine

[gobi]

I wanted to use my ResMed while I on the road.

I started out with this solution:

1. 12 Volt ResMed power adapter (bought online)
2. A 90ah vehicle starting battery I had laying around.

Worked but heavy - The 31d battery worked fine for 3 nights of use, but that thing was heavy, and I had to take it out of the van to charge it.

After I had to lift and move it few times I was ready for a lighter solution.
I bought a 100ah Litto Kala lifepo4 battery (well I made it myself )

ResMed CPAP > 12 Volt Power Adapter > 12v 100ah Lithium battery

Next in my list is to set up a charging link so I can use it to charge the 100ah Lifepo4 battery from my van's alternator.
I will be charging @ 10a max.
The 100 ah battery is used to power my laptop using a small 200w inverter. So this little battery gets a lot of use.

 

[AutoMechanic]

Nice . My dad used to have one of these machines. He had a plug that plugged into the cigarette lighter for his so he could use it in his truck when he slept at night. Smart idea.

 

[Wayne]

A 90ah vehicle starting battery

Was that out of a jump-starter?

 

[gobi]

Was that out of a jump-starter?

lol, no, I had a smaller AGM batt (acdelco) that died under warranty, took it to the distributor and he did not have a little one, instead paid the diff (30$) for the biggest baddest AGM they had in stock

 

[Wayne]

So it's an automotive type AGM? Picture?

 

[gobi]

Auto, but I was shocked they had this in stock and it was fresh stock.
The weight just makes it a semi portable unit.

 

[Wayne]

Thanks, a picture is worth a thousand words!

 

[gobi]

Which battery to get for CPAP machine is a subject that we all have stumble with.

First let's look at 8 hours of use at 8 pressure setting and 6 Humidity setting.

Average AH need for this use for 1 night = 20 to 25 AH @ 13v

Lithium batteries give us around 80% usable capacity.

So, I went with a 100 AH @ 13v lithium battery. This will give me 3 days of use before I have to charge it.

So what are the choices out there:

1. If you are handy, buy 100 ah littokala cells off aliexpress and add your own BMS = total cost $200, this is the route I went.
2. Buy a 100 ah @13v premade battery off Amazon, Miady or any of the popular inexpensive brands.

 

[gobi]

For dry camping and for travelling down south to fish in my van camper, I wanted to figure out the optimal size for my battery for CPAP machine in my camper.

I bought a factory (RESMED) 12v power supply for my CPAP as I did not want to buy an inverter and use the 120v power supply that came with the CPAP.

I sleep 6 to 8 hours on average, so using a killwatt meter I figure out max around 300wh

How much battery for 1 night:
300wh/14 = 21 ah at 14v,

14 volt is the output of a LIFEPO4 12v battery give or take 0.5 volts.

So a 50ah 12v LIFEPO4 battery will be sufficient for 2 night and then recharged.

My go to LIFEPO4 battery right now is a 100ah 12 battery.

I have attached a pic of the RESMED12v power supply, is comes with 12 female cigarette receptacle that has rings to be connected to a battery.