An hour of charging every other day will usually be more than enough.  The reason for every other day is how a lead-acid battery charges.  It will accept more amps more quickly when it is below 80% SOC than above that - in other words, you can charge it from 50% to 80% much faster than you can from 80% to 100%.  So you'll get more amps into the battery per gallon of fuel you burn by doing it every other day, and then only getting it back up to some point below 80% SOC.  Not getting it to 100% is fine until you hit that 7-day mark, then you need to do it.

So a typical week boondocking might give you this SOC per day, assuming 20% used each day:

Monday morning 100

Tuesday morning 80

Wednesday morning 60, 1 hour charge back to 80

Thursday 60

Friday 40, 1 hour charge back to 75 (note more amps put in during this hour)

Saturday 65

Sunday 45, 1 hour charge back to 80

Monday 60, several hour charge back to 95-100

Repeat the next week

And a wallet size photo of Techntrek...the early years:

 

My situation is this-    210 AH of AGM batteries, two each group 31 at 105 AH each.

Overnight CPAP uses about 60 AH.  

Other loads throughout the day, constant drain from refrigerator electronics (I miss the old electromechanical thermostat)*  plus occasional light usage plus water pump plus constant drain from "entertainment center" (to which I'm going to add a true on/off switch)  plus phone charging plus computer use etc-

 I figure all this can easily add up to 70AH per day, probably more than that really..

 

So the AGM manufacturer recommends a max charge rate of about 60 amps...so I'd be able to more than bring things up fully in 2 hours- except- the charger in the r-pod can't deliver 60 amps, more like 25-30 I figure but I'll have to test that to be sure....the WFCO in my previous camper (Aliner) nowhere near put out rated current for charge.

 

So if one camps long enough, and I've done up to 14+ days in the past-  I can't put enough back to stay ahead.  The full top off after a week would be nice- except if the campground has a generator limit- where you can't do it in the time alotted...

 

My point was by minimizing usage one can go more days before it is an issue....and with the cost of 210 amp hours of AGM, about $400, I want to extend life as long as possible 

 

 

*one additional caveat of electronics-  we were camped in the mountains of NC with NO hookups- lightning hit a nearby tree and fried the board in my Norcold fridge-  classic EMP.    No fridge the rest of that trip and a $200 board bought when we got home.   Sigh-  old mechanical bulb t'stat would have just kept on working 

Being an electronics guy I figured I'd troubleshoot the old board using the new board as a guide and have a spare for next time- NOPE they changed the design..

 

 

I probably won't buy AGMs again- they were bought for a special need in a different camper so I already own them...I much prefer 6v GC batts in series-  I've proved to myself many times over the most AH for the dollar is derived that way- at least in my experience. 

 

Budward - I have a similar problem right now, I'm sure I need a new control board.  You are right the old style fridges would just keep moving along...and don't need constant 12 volt input.  This is one area where I feel camping technology has actually gone backwards through their efforts to "improve" it.

Are you sure about the actual amp draw from your CPAP?  I'd bet it is labeled @ 5 amps but that is only because of the startup current for the motor.  Once running it probably isn't using more than an amp.  Unless you are using the humidifier which is just a big heating element and that will use several more amps.

http://www.thecpapshop.com/resmed-s9-series-cpap-dc-power-converter - http://www.thecpapshop.com/resmed-s9-series-cpap-dc-power-converter

I know everyone is different, but in the five years I've been using my CPAP, I can easily go days without the humidifier and still enjoy the benefits. The savings in power are significant. I can run my ResMed S8 for 2 nights on a 11AH booster battery and everyone sleeps well. The humidifier/heated hose is a luxury, IMO. There are also oral appliances worth exploring.

fred