Battery Charging question - WFCO vs dedicated Battery Charger

[Riverbug]

Wow, you must be lucky (or I'm not lucky)! Before I switched to LiFePO4, I was barely able to get a night from my original battery. There were a couple of times I had to hook the jumper cables to my truck battery just to get the slide in in the morning. Was my battery bad? Maybe, but I didn't care anymore since I made the lithium upgrade.

I was right there before I switched too. The battery that the dealership provided had an AH rating of 25. I didn't know they came that low.

[Redapple63]

Greetings:

I am looking for some advice on the best way to recharge my batteries.

- 2021 22MLE with WF-8735 converter / charger
- 1 75ah AGM, adding a second battery (still deciding on a second 75ah AGM or maybe a Lithium)
- Dry camping for 2-3 nights occasionally - for the purpose of my question let's use the example of 3 nights in Rocky Mountain National Park in July (no hookups)
- I have an inverter generator - generator hours are 7:30 to 10 and 4-8:30
- Want to run furnace all night and then recharge during the day

So...

I have read info on running a furnace all night on batteries ~6.5amp per hour when furnace is running etc.

I am concerned that even if I can run the furnace all night, propane fridge and occasional LED lights and water pump - I won't have enough generator hours to charge the batteries back up.

So is it faster to use 2 dedicated battery chargers (say 8 amps) or run the batteries in parallel (get a second matching AGM) and have the WFCO do all the charging?

I have thought of getting a second Lithium (since they charge faster) and run the Lithium all night and switch back to the AGM during the morning generator hours and and charge the Lithium during the day since it will charge faster?

I honestly believe for the amount of camping you are doing, going with two gc2 6v batteries would meet your needs. Two of these batteries should take you through 2-3 nights with your genny for a couple hours a day. Much cheaper entry point. If you plan on doing longer boondocking type trips then look into more robust options like Lifepo4 or solar.

Bill

[Scott'n'Wendy]

Scott 'n' Wendy say you won't run the battery down in 1 night.
BTW - I asked the WFCO guys how many amps they charge at (I wanted to compare to the 8 amp charger I have and they said:

"Hi Daniel,
The output is variable, up to 35 amp, and depends on how discharged the battery is."

I asked then again - 35 amps?? I thought that was not too good for a FLA or AGM to be charged like that.

They said all the power will go to the battery less any other consumers (lights, pump etc.) that happen to be on.

Honestly, I find that hard to believe. So if I plug into my generator and I get 35 amps going to the battery, seems like it will charge in no time. Comments welcome on that one.

Just to be clear, I said I make it through the night on the cheap dealer battery..the fridge and furnace will still be working, but it will be run down and the gennie needed to charge it in the morning.
From everything I've read previously, 35 amps going into a LA/agm battery will shorten it's life.

[xrated]

Just to be clear, I said I make it through the night on the cheap dealer battery..the fridge and furnace will still be working, but it will be run down and the gennie needed to charge it in the morning.
From everything I've read previously, 35 amps going into a LA/agm battery will shorten it's life.

A FLA battery will only charge as much as the battery allows it to recharge, based on the internal resistance of the battery itself. FLA batteries have a much higher internal resistance vs. a LiFePO battery. So it really doesn't matter if you have a 35A charger, a 55A charger, or whatever size. Charging voltage and the internal resistance of the battery is what determines the charge rate.

Current = voltage divided by resistance. So an example. a 35 amp capable charger is putting out let's say 13.8 volts for charging, and the internal resistance of the battery is .69 ohms. Charging current is 20 amps.
Now you have upgraded the charger to a 55 amp capable charger and it puts out 13.8 volts. Let's assume that nothing has changed as far as the battery is concerned and is still .69 ohms internal resistance....so again....13.8 volts divided by the .69 internal resistance of the battery.....20 amps of charging current is flowing. The battery internal resistance is what determines the charge current if two different chargers are used that have different AMP CAPABILITIES.....but put out the same voltage. Hope this helps.

[Ynot4me2]

Small detail the WF-8735 is a 30 amp charger so is the PD replacement. If you have a clamp meter, you could drain you original LA a little and then plug to shore power and measure how many amp are actually going to the battery.
If budget permits, of course, instead of buying another LA or even 6v, I'd go straight to Lifepo4. It's the one that will give you the bigger bank capacity and less foot print and weight. You don't have a lot of generator time to recover what you've consumed so you need to increase your bank to compensate.

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[Always Learning]

debarks, here are some real life usage numbers for running furnace. Hope it helps.

My furnace draws about 8 amps.
We have two 100ah Battle Born Lithium batteries.
Yesterday we pulled into our dry camp in Colorado. Air temperature about 60 degrees and after a day of travel the inside trailer temp was at ambient temperature.
Started with fully charged batteries.
Usage
Heated the trailer from ambient then kept it good and warm until we went to bed, 10pm and set the thermostat to 58. Overnight low was 31 degrees. We had our normal light usage and device charging over night.
No inverter usage.
At 6am this morning we had used 55ah

Edit: Second night we use 40ah. The first day was heating the trailer after travel and the second day the trailer was warm from solar gain and use during the day.

[Redapple63]

I am sticking to my original proposition, go with the two gc2 batts. Lifepo4 is expensive start point for occasional 2-3 day trips (although they have come down significantly in price).That will give you approx 110 usable amp hours. All in for a Couple hundred bucks, maybe $250..

I would endorse different path if the op camped more, maybe that is something they can “grow” into.

Bill

[xrated]

I am sticking to my original proposition, go with the two gc2 batts. Lifepo4 is expensive start point for occasional 2-3 day trips (although they have come down significantly in price).That will give you approx 110 usable amp hours. All in for a Couple hundred bucks, maybe $250..

I would endorse different path if the op camped more, maybe that is something they can “grow” into.

Bill

Bill, it's not just about the AH and Cost. LFP batteries save weight, especially if the batteries are up front (tongue weight), they will also last a lot longer than FLA batteries (+3500 cycles of charge/discharge), there is no adding water (FLA) like many of the 6V GC batteries require, and there is zero concerns about off gassing.....which means you can move them into the camper if you need or want to. Just a few things to add to the discussion....YMMV.

[Redapple63]

Bill, it's not just about the AH and Cost. LFP batteries save weight, especially if the batteries are up front (tongue weight), they will also last a lot longer than FLA batteries (+3500 cycles of charge/discharge), there is no adding water (FLA) like many of the 6V GC batteries require, and there is zero concerns about off gassing.....which means you can move them into the camper if you need or want to. Just a few things to add to the discussion....YMMV.

Absolutely agree, great points!

[dbarks]

Great comments - thanks all.

- 55ah will be the nightly bogey
- I appreciate the charger/resistance knowledge. I have never heard of what the internal resistance is of a battery to even make the calculation. Frankly, the WFCO internet folks were not very helpful trying to explain this to me. Probably didn't know themselves.
- The tricky part here is balancing doing one 3 night stint a year vs cost. If we boondocked all the time I would buy more than I need. Buying a $500-$600 battery(s) for one trip and then have it sit on my workbench all year is not too great. Even if money is not an issue this seems like a waste.
- As I said, cutting this too close is not an option.
- I looked at using a propane Mr Buddy (may have the name not quite right...) for heat during the night and this solves my power issue. I have to admit I am not quite comfortable with burning a portable propane heater inside. Something goes wrong and it will make my one use battery sitting on the workbench seem like the best idea ever...

Also - I like the idea of 2 separate batteries. I run one in the evening, switch to one for overnight, then switch back in the mornings. It give me a bit of a back up if the second one dies in the middle of the night. Having a single bank has no redundancy. This is of course a personal preference.

Thanks again, really good information to help me figure this out.

Dan