Camping CPAP Battery Runtime Calculator

For anyone who’s ever camped out deep in the woods and panicked as the sun sets, there’s no mystery here: it dawns on you that your CPAP may die before sunrise. It is not because you’ll lose any Zzzs, but because you’re going to be terrified of suffocating in the dark with only a barely-readable phone screen to guide you. Of course, most folks bring a large battery and cross their fingers. More often than not, this is a bad plan. Why? They don’t understand the nature of what they’re powering. Is the issue insufficient capacity? No, typically, it’s not. It’s simply a failure to appreciate what happens to all that juice along the way. Once you know your devices parameters, our calculator does the rest. No more wild guesses at temperature effects or conversion losses.

A CPAP machine is no light bulb. A huge part of the runtime issue come from the comfort features, which do most of the heavy lifting, but remain quiet as the silent killers of runtime. Specifically, things like humidifiers and heated hose pull a ton of juice because they’re basically tiny space heaters by your head. Solution: Turn off the heat and go to bed in a dry tent. Thing you can’t turn off? The pressure. The table shows how adding a heated hose to your set-up can almost triple your electricity usage different than using a basic travel machine. So there’s that comfort/morning thing vs. You also have to consider the overnight length equation. When you’re camping in July, maybe you don’t need the heat. But when you’re camped out in January, you do, except now you need a larger battery too.

How to Make Your CPAP Last Longer While Camping

After that comes the power path. How you connect matters as much as what you connect. Most people say to use a simple AC inverter. Why not? It’s convenient, right? It taps the batteries, converts that battery power into household current, then spits it out to the wall brick. Sounds convenient. Sounds easy. Is wasteful. An inverter doesn’t get everything done; it loses some energy as heat. An inverter may only be eighty-five percent efficient. Some is worse. And some inverters draw power all the time, even when they’re not hooked up to anything. When you unplug, an inverter can sip away enough electricity in eight hours while you’re sleeping to equal the amount needed to run a blower for two hours.

Bypassing this whole thing is direct DC connection. If your machine has a twelve-volt port, hook it up. Instead of losing twenty-five percent of that energy, you’ll retain ninety-five.

This equation is also affected by the chemistry of the battery. One-hundred amp-hour sounds like a lot. But as long as you’re camping in the cold, that’s a lie. Lead-acid batteries suffer in cold weather and lithium holds up better, but both types of batteries still struggle in freezing temperatures. A battery will deliver maybe half of its rated capacity at zero degrees Fahrenheit. This derating is accounted for in the calculator, but you must be honest with it regarding the temperature. Is your battery outside your van? It’s cold. Is it inside your sleeping bag? It’s warm. And often, that’s the difference between waking up at three AM to a dead machine or a full night of sleep.

Another trap is state of charge limits. For example, you might think a one hundred percent charged battery gives you one hundred percent of the energy, but it does not. Wrong! Deep cycling a battery to zero eventually damages it. To extend battery life most experts suggests shutting down at ten or twenty percent. So a one hundred amp-hour battery only provide about eighty amp-hours of usable energy. Failure to plan for this buffer will make your math always optimistic. The tool allows you to set a reserve. Plan smartly for unexpected delays and bad weather.

Here’s what we think is the best bet: Measure yourself. Average estimates from manufacturers don’t account for your tent. Manufacturer averages don’t apply to your specific tent. Run a normal night of sleeping on your machine. What was the humidifier set at? Did you have your hose heat on? What were your temperatures and voltages on your batteries? The chart above will run the numbers for you. It eliminates the guessing game. It reveals exactly how many nights you can survive with your current setup.

If it’s too few, then you have options. Drop the humidity. Switch to DC. Buy a bigger battery. You should of not done all three. Just plug the biggest hole in your system. Once you stop ignoring the hidden leaks, the math becomes easy. Sleep well.