Please help me figure out this camping battery stuff

[idamtnboy]

The best power to price option is, as Archangle said, a wet cell deep cycle battery. How many nights will you be camping? I think with your CPAP you can probably get 4 or more nights from a 115 amp-hr deep cycle. The overall lowest cost and least troublesome approach is to buy one battery for every 4 nights you'll be camping. Charging a deep cycle while camping isn't easy. A few years ago I tried charging a a deep cycle from my pickup while camping. I had cables and power connects set up so that all the charging current from the alternator would go to the battery. It still would have taken 3 to 4 hours of run time to get the battery recharged even from only one night's use. I attribute that to the design of deep cycles in that they are not built for high current flows, either in discharge or recharge. It became apparent to me that DC batteries like to receive a long low rate charge, not a short high rate like a car battery will take. The next best option I have thought about is to buy a small inexpensive generator from Harbor Freight and use it to recharge the battery. The usual best price for one of them is about $90, the same as for a 115 AH battery. But you're looking at 2 to 4 hours run time every day for a full recharge, with all the attendant noise and such.

Is this camping trip a one time event? Even if it's an annual affair consider buying one or more new deep cycle batteries, enough for the whole outing. Afterwards sell them. I would guess you could sell a DC battery used one time for at least 3/4 of the new price. If you keep a DC battery it won't last for more than 4 or 5 years unless you have some way to put it to regular use. One or two deep discharges and recharges per year borders on battery abuse. I had one that was only 3 or 4 years old and was good for only 2 nights. A new one was good for 3 1/2 nights.

This last fall I went on a 4 week trip on my motorcycle pulling a tent trailer. I slept in the tent about 1/2 or less of the time. I have a charging circuit from the bike to the DC battery in the trailer. As far as I could tell the battery was always fully charged at the end of the day, but that was with the bike charging the battery for 8 to 10 hours of travel time.

The best way to gauge the charge level is with a hygrometer. But the first year I used batteries for camping I did not get good reliable results that I could really depend on to let me know the exact charge level of the batteries. I'm not sure why. I just know that keeping track of the charge level of the battery isn't easy. Don't try to use voltage. Voltage drop is not linear to charge level. I drops off slowly at first and then very quickly toward the end.

[CapnLoki]

The best power to price option is, as Archangle said, a wet cell deep cycle battery. How many nights will you be camping? I think with your CPAP you can probably get 4 or more nights from a 115 amp-hr deep cycle. The overall lowest cost and least troublesome approach is to buy one battery for every 4 nights you'll be camping. Charging a deep cycle while camping isn't easy. A few years ago I tried charging a a deep cycle from my pickup while camping. I had cables and power connects set up so that all the charging current from the alternator would go to the battery. It still would have taken 3 to 4 hours of run time to get the battery recharged even from only one night's use. I attribute that to the design of deep cycles in that they are not built for high current flows, either in discharge or recharge. It became apparent to me that DC batteries like to receive a long low rate charge, not a short high rate like a car battery will take. The next best option I have thought about is to buy a small inexpensive generator from Harbor Freight and use it to recharge the battery. The usual best price for one of them is about $90, the same as for a 115 AH battery. But you're looking at 2 to 4 hours run time every day for a full recharge, with all the attendant noise and such.

Is this camping trip a one time event? Even if it's an annual affair consider buying one or more new deep cycle batteries, enough for the whole outing. Afterwards sell them. I would guess you could sell a DC battery used one time for at least 3/4 of the new price. If you keep a DC battery it won't last for more than 4 or 5 years unless you have some way to put it to regular use. One or two deep discharges and recharges per year borders on battery abuse. I had one that was only 3 or 4 years old and was good for only 2 nights. A new one was good for 3 1/2 nights.

This last fall I went on a 4 week trip on my motorcycle pulling a tent trailer. I slept in the tent about 1/2 or less of the time. I have a charging circuit from the bike to the DC battery in the trailer. As far as I could tell the battery was always fully charged at the end of the day, but that was with the bike charging the battery for 8 to 10 hours of travel time.

The best way to gauge the charge level is with a hygrometer. But the first year I used batteries for camping I did not get good reliable results that I could really depend on to let me know the exact charge level of the batteries. I'm not sure why. I just know that keeping track of the charge level of the battery isn't easy. Don't try to use voltage. Voltage drop is not linear to charge level. I drops off slowly at first and then very quickly toward the end.

I generally agree with most of what you're saying, but I have a few issues: The OP has only mentioned 2-3 nights, so a larger deep cycle battery really isn't needed, especially if humidity is not needed while camping. And with the price of AGM falling (I saw 75 AH on Amazon for $147) I don't see any reason to use a flooded battery if its not in a secure environment, such as mounted in a camper or boat. And although I use a hygrometer a few times a year, I don't recommend on a weekend camping trip. Even just adding water to a flooded battery is one of my least favorite tasks.

Deep cycle flooded batteries will accept about 25% of their rating when recharging (AGMs are even better), until they get up to about 80%. In other words, a 100AH battery should accept 25 Amps if the right voltage is used. The standard protocol for boats (and I think RVs) is to discharge to 50%, then recharge to 85%, which should take about 1.5 hours. Battery banks are sized to about triple the daily use so that this cycle can be done once a day. I don't know why yours didn't charge faster, except that one night should have only discharged about 10%, and topping off the battery can take a long time. Its also possible your alternator/regulator isn't putting out enough or you were idling instead of revving up.

[blakepro]

Thanks for the replies. The family camping trip is kind of an annual thing, although once I get the battery setup all figured out, I could see going camping with my wife and kids occasionally. I expect most camping trips to be 2-3 days at most. Although I am interested in seeing how many nights I could get out of the battery if I use minimal comfort settings and really tried to get the most nights out of it.

This is what I ended up buying and am testing with.

I bought this 12V 35Ah sealed deep cycle battery. I liked that I didn't have to worry about it leaking. Truthfully, I know little about big batteries and its one of the main reasons I started this thread. I bought it mainly on CapnLokis recommendation. So far I've been pretty impressed with it.


I then got the Battery Tender plus to charge it with and to use its cable system. It comes with a fused quick connect wiring system that I attached to the battery and will leave connected.


I got this cigarette adapter quick connect that is compatible with the Battery Tender system


I got the official respironics DC cord. One thing to note, it comes with 3 fuses. a 3Amp, 5Amp, and 7Amp. It comes with the 3Amp one pre-installed. When I attempted to use my machines humidifier with that 3Amp fuse installed, it blew the fuse. I've been using the 5Amp one without any problems, even at full humidity settings.


I'm using this thing to check voltages even though I know its a poor indicator of actual Amp Hours left/charge level. (Its pretty much all I have and I cant really afford better alternatives)


And finally, I bought a male to male Cigarette socket cord in hopes that I might be able to connect the battery to my cars plug while driving around during the day to add some sort of beneficial (although probably minimal) charge.



One question I have is: will the initial testing that I'm doing right now seriously harm my battery? I ran it until my machine stopped working (2 nights, about 11 hours). I plan to do that about two or three more cycles to get a baseline of how long my machine operates at humidity settings of 5, 3, 1 and zero. So that would be about 4 cycles of pretty deep discharge. I have no idea how deep, but the c-pap machine refused to work once it got down to 6.5 volts. I plan to use these baselines in my camping planning. Knowing how many nights I need, I can turn down comfort settings to match my time needs.

[Pugsy]

I plan to do that about two or three more cycles to get a baseline of how long my machine operates at humidity settings of 5, 3, 1 and zero.

Can you keep us posted on this experiment in terms of humidity use? When I experimented I wasn't able to get one minute longer battery use with changing the humidity setting down to 1 from 5...and I was unwilling to go to 0 and be miserable just for an experiment. I was miserable enough using 1 for 4 1/2 hours.
I am just curious if anyone else actually can get more life with just a reduction in humidifier setting vs turning it off.

[CapnLoki]

One question I have is: will the initial testing that I'm doing right now seriously harm my battery? I ran it until my machine stopped working (2 nights, about 11 hours). I plan to do that about two or three more cycles to get a baseline of how long my machine operates at humidity settings of 5, 3, 1 and zero. So that would be about 4 cycles of pretty deep discharge. I have no idea how deep, but the c-pap machine refused to work once it got down to 6.5 volts. I plan to use these baselines in my camping planning. Knowing how many nights I need, I can turn down comfort settings to match my time needs.

The conventional wisdom has always been that 100% discharge is not good. However, most of the "Cycle Life v Depth of Discharge" charts I've seen for AGM show several hundred cycles for 100% DoD, so I wouldn't worry too much about bottoming out a few times. However, I wouldn't plan on 100% discharge every time you use it - if you can leave 20% in the tank there will essentially be no wear. I couldn't find a cycle life spec for Motobatt, but I would recommend Googling "AGM Cycle Life v Depth of Discharge" for a host of info about this stuff.

[blakepro]

I plan to do that about two or three more cycles to get a baseline of how long my machine operates at humidity settings of 5, 3, 1 and zero.

Can you keep us posted on this experiment in terms of humidity use? When I experimented I wasn't able to get one minute longer battery use with changing the humidity setting down to 1 from 5...and I was unwilling to go to 0 and be miserable just for an experiment. I was miserable enough using 1 for 4 1/2 hours.
I am just curious if anyone else actually can get more life with just a reduction in humidifier setting vs turning it off.

Okay. So my first experiment yielded 11 hours of use with my settings on a 5 humidity level.

My second round was tested on a setting of 3. Here are the results:

Volt reading - Notes
13.2 - Fully charged right after taking it off of the battery tender charger
12.3 - After first night at 3 humidity setting - 7.5 hours of usage
(forgot) - Second night of usage (3 setting) - 7 hours of usage (DIDN'T DIE ON SECOND NIGHT LIKE IT DID AT A 5 SETTING)
6.4 - Died - (3 setting) - Died after 1.5 hours of usage

So thats 16 hours of usage with a setting of 3. So I can get 5 more hours hours by reducing humidity from 5 to 3. My next attempt will be a setting of 1 next weekend. (If I can tolerate it)

So, to sum it up. The current findings are:
Using a PRS1 50 Auto set. Pressure range 14-15. I get the following usage hours from this battery setup:
Humidity setting (PR1 humidity) 5: 11 hours
Humidity setting (PR1 humidity) 3: 16 hours