Is this a good power backup plan? See picture.

[king_alvaro]

It is rare to have power outrages in my city. But just in case. I plan on using the car battery of a Honda civic. I will use an old Resmed machine I have. My pressure will be at 9, for 8 hours and no humidifier and I plan to use it one night. The battery has 500 cranking amps. That is what the battery stated. Do you think it is a good idea?

I don't have the money to buy a deep cycle battery.

[-tim]

A "deep cycle" battery is just one that will last longer if you run it way down lots of times.

[GumbyCT]

Do you think it is a good idea?

So much depends on the health of the battery. This is not that big a battery but I would say try it to see if it will fit your needs.

Always try your setup at home BEFORE going camping or using it bc the power went out.

[HoseCrusher]

To get an idea of how well it will work, charge the battery then let it sit for 4 hours or so. Next drag out your voltmeter. If you don't have one, borrow one... or buy one.

With your voltmeter attached, turn on the machine and let it run for awhile. Note the voltage on the battery. If you take some data points you should be able to establish a trend of how fast the voltage drops. After the initial drop, the voltage should trend linearly downward allowing you to estimate the total run time.

Under load, 10 volts is a good place to stop to prevent damage to the battery.

Remember to immediately charge it back up.

Cranking amps are different than amp hours. You are interested in amp hours, if you can find that specification.

[Dan Jacobs]

In an emergency, any battery will do. If this is all you have and/or all you can afford, than it's what you have, and you have to make the best of it.

The battery you are using is designed to start a car. It is designed to give a large current load for a short amount of time. It will run your machine, but draw it down too much, which is surprising a small amount, and irreversible damage is done. The plates inside the battery will actually begin to deform and ripple. Deep cycle batteries are designed to be drawn down to a low State of Charge (SoC) and recharged with minimal damage done to the battery.

Read this for more information if you want it:
viewtopic/t79218/Batteries-Knowledge-is ... lasts.html
You don't have to know about electronics if you just stick with the highlighted info, but there is more info in there if you want it.

Good luck!

[archangle]

That kind of inverter would damage an S8 humidifier, so I'm guessing it would damage an S7 humidifier as well.

Since you don't have a humidifier, you're probably OK.

A single night's usage, followed by recharging, done occasionally will probably be alright.

One risk is that batteries can just die on you. It's bad when you need it and find it's dead.

Don't leave it hooked up to a charger all the time unless you get a good "floating" charger.

[Linus]

Put the battery in a battery box. This will protect you in case it explodes. I have run on a car battery during power outages without issues. The only difference is that I recharge my battery during the day when I am running my generator. If you have an extended power outage, find a way to keep the battery charged.

Keep the battery on a maintenance charge as backup.

[JohnBFisher]

You can use the following Battery Backup Design to create your own battery backup system:

viewtopic.php?p=449334

This design puts the battery in a battery box, it keeps things securely fastened, it includes a float charger, and makes the whole arrangement much safer.