Using unit with a 12 volt battery.

I am new to this forum so thanks for allowing me in.

My question is this:
Can I run my unit for approx 9--10 hours on a 100 amp glass gel battery?
Yes I like my sleep.
This would be used in a caravan and we would like to stop "off road" on some nights.
The hand book talks of it drawing 6 amps, but I don't really know what that means.
My uneducated mind reasons if I have 100 amps and it draws 6 amps it should last for approx 15 hours.
Has anyone had experience with this?
Thanks Malandi in South Australia.

If you have a 100A 12V deep cycle battery, then you can plan on getting perhaps 70-80A out of it, and at 12V that's 840-960 Watt Hours.

Most newer typical CPAP machines use less than 100W even with a heated humidifier and hose, so this battery should supply your needs all night before you have to recharge it. If you don't use the humidifier and heated hose it may last several nights before you have to recharge it.

If it's a regular car battery, then you should only use about 1/2 it's capacity before recharging, about 600 watt hours. Depending on your exact CPAP and setup, you might be able to get 6 hours of use from it with the humidifier and heated line, and much more without the humidifier and heated line before it needs to be recharged.

Please keep in mind that these are very, very rough estimates and without knowing exactly what machine you have and how it'll be used and set up, we can't really give you much help.

Also note that many machines can't run off a battery without a machine specific adapter or DC-AC converter, so make sure you investigate how you're going to run the machine from the battery, and that the manufacturer supports this use.

If you provide your machine, humidifier, and other setup information we may be able to provide you with more specific information.

If the machine will run on 12 volts DC, you can expect more time than if you have to use an inverter.

Malandi wrote:I am new to this forum so thanks for allowing me in.

My question is this:
Can I run my unit for approx 9--10 hours on a 100 amp glass gel battery?
Yes I like my sleep.
This would be used in a caravan and we would like to stop "off road" on some nights.
The hand book talks of it drawing 6 amps, but I don't really know what that means.
My uneducated mind reasons if I have 100 amps and it draws 6 amps it should last for approx 15 hours.
Has anyone had experience with this?
Thanks Malandi in South Australia.

OK - As a welcome to our group I offer a quick tutorial. But first, the answer to your question is: yes, your battery probably will easily handle one night.

Battery capacity is measured in "Amp-Hours," as in a 100 amp-hour battery will provide 100 amps for one hour, or 10 amps for 10 hours, or one amp for 100 hours. A "car battery" sized battery, weighing about 50-60 pounds, will have a capacity of about 100 Amp-hours. Car batteries, however, are designed for starting cars and will fail prematurely if used for an application like a cpap. You should look for a "deep cycle" battery. In particular, don't run your cpap all night from the car battery and expect the car to start in the morning! Batteries come in flooded (old style), gel, and AGM (Absorbent Glass Mat). AGM batteries are preferred because they are totally leak proof, but they are a bit pricey. If your caravan is setup with a battery it is probably deep cycle.

Most cpaps use roughly 1 amp or less so in the course of a night they use about 8 Amp-hours or less. Mine is about 4 amp-hours per night. The humidifier can be more costly, between 5 and 25 Amp-hours per night. The power supply (usually a small brick that plugs into the wall) will often have a larger value like 50 to 90 watts, or 5 amps because it has to cover the worst case startup values.

If your pump is Respironics it can take 12V directly with an inexpensive cord; if ResMed a 12 to 24 Volt adapter (about $85) is best; otherwise you'll need an inverter which is not very expensive but is only 60% efficient so your battery won't last as long.

Lead acid batteries (which includes almost all starting and deep cycle batteries other than Lithium) should not be discharged more than 80% or they will die early. The wear is proportional to "depth of discharge" and as mentioned, starting batteries are the most sensitive, and shouldn't be discharged more than 20% if you want them to last a long time. So be conservative in your estimates. That said, you might easily get up to a week if you don't use the humidifier. Tell us your exact setup and we'll be able to advise better.