Charge spare battery

[K_and_I]

My wife and I both use CPAP machines. When we are at electric sites, no problem. When we do an overnight without hookups, it becomes a problem. The CPAP batteries run over $200 each, so over $400 for us both. I already have an inverter big enough to run both machines. I bought an AGM battery big enough to run both machines through the inverter for a night, but am unclear as to the best way to recharge it when I get a plug in site. Can I jump it to my camper battery and let the converter charge it, too (Progressive Dynamics converter), or do I need a stand alone charger? Thanks for your help.

[wa8yxm]

K_and_I wrote:
but am unclear as to the best way to recharge it when I get a plug in site. Can I jump it to my camper battery and let the converter charge it, too (Progressive Dynamics converter),

Short answer YES:

Longer answer. Why not upgrade RV house batteries and use them instead of the portale

I suggest at least one (or two) pair GC-2 golf car batteries if you can mount them.

[K_and_I]

Thanks again for the replies. They are Resmed CPAPs and use 24 volts. We do plan to turn off the humidifiers- that is the basis of the calculations I used to size the battery. Things may change in the future, but for now, I just need 1 night's worth of use at a time. We do not boondock for more than 1 night without a plug in between.

[Sam_Spade]

ktmrfs wrote:
if you don't need the humidifier, turn it off.

This.

And.....when it comes time to replace the CPAPs, get one that actually runs on 12 V and get the appropriate power cords to do that.

As for charging the extra battery, if you are parked at a campsite that has power service, it likely has 30, 50 and 15 amp outlets.
Get a charger in the 15 to 20 amp range and plug it into the 15 amp outlet.

Not only will that solve the recharging problem but then you will have a charger for other things when you need one.

[ktmrfs]

if you don't need the humidifier, turn it off. My cpap draws less than 8AH per night w/o humidifier, that will last many nights even with two cpap machines. with humidifier, power drain will depend a lot on amibient temps and how much heat it needs.

And, unless your cpap is really old, it will run on either 12VDC or if it is a resmed, 24VDC. for 24VDC there are several dc-dc converters for the resmed.

In reality virtually all the cpaps today run on 12 or 24V, the 120V plug either has a 12V brick inline or the cpap takes the 120V isolates it for safety and routs it to the DC input on the CPAP.

[ksbowman]

A friend of mine tent camps when hunting and uses a 12 volt battery for a week at a time for his CPAP. He uses a small solar charger that is for a fence charger. It is only about 5x7 and does just fine.

[sgip2000]

What brand are your machines?

Most brands have a 12v adapter available which would be more efficient.

[K_and_I]

Thanks for the replies. I don't plan to try to charge while driving, but I understand the isolator concept.

[time2roll]

Yes PD will charge it just fine. Connect in parallel first, then plug in.

[Michelle_S]

You can purchase a "Battery Isolator" which will allow the spare battery to be charged when on shore power or from the TV, if setup properly, during travel. But the Isolator will prevent the spare from drawing juice from your RV battery.