A year or so ago I was diagnosed with sleep apnea, and since them I’ve been sleeping with a CPAP. This past weekend, I joined my daughter on a scout camping trip to a campground without readily accessible electricity. This would be the first time I found myself in this situation, and as the date approached, I realized I was going to have to build or buy some sort of battery solution for my CPAP. I opted for the “build” option because it seemed like a fun project.

This is what I ended up with:

It has a pair of 10Ah SLA batteries, two 12V ports, two USB charging ports, and an integrated 4A charger (just plug in an extension cord and it’s all set). There are fuses on all of the output ports.

Batteries

I spent some time looking at battery options. I wanted something that would easily last a couple of nights. According to the documentation from ResMed, my AirSense CPAP draws around 1A when the heat and humidity are disabled. That means for two nights, with the heat and humidity off, I’ll need at least 16Ah.

I looked at some LiFePO4 batteries, but they were typically two- to three- times the cost of an equivalent SLA battery. I ended up purchasing a pair of 10Ah SLA batteries. Testing confirms that it does last for two nights. With the integrated 4A charger, they charge up relatively quickly as well (for a single night of use, it took around an hour for a full charge).

The batteries are held in place by a roughly U-shaped piece of wood on the bottom of the case. The charger and the foam bad hold the batteries in when the top is closed.

ResMed battery data

ResMed battery data

Parts list

Panel design

I used qcad to design the panel layout. The cross-hairs are for identifying the center point:

I used a 1 18” hole saw to make the holes for the 12V and USB ports and a 2” hole saw for the through-plug on the back. I used a step bit to drill the smaller holes for the switches.

A few extra pictures