Burl -- 2003 GMC Safari soon to be camper

[AstroWill]

I was wrong, it's only 83lbs. http://cogenient.com/mfc-refdocs/C&D%20 ... 90MRLP.pdf

Says 115Ah when new, so you could have used 57Ah @50%DoD when it was new, slightly less now.
Looks like a good AGM!

[Rod's Trucks]

Please also note that 115AHr rating was based upon a 20 Hr discharge cycle, and at 77 degrees F. (25 degrees C)
That is not a very likely scenario for most applications we might have.
I have a couple of very similar C&D UPS batteries (12-475FR's )for radio purposes. They are very good batteries, and will last a long time if one takes good care of them.
Rod J
Issaquah, WA

[SportsBoy]

I've been having a hard time trying to figure out what type of battery setup to go with, since I'll be doing plenty of winter camping too.
Seems like agm and lithium both are weak in the cold in their own ways. I don't want to add battery heaters but that may be necessary, in which case might as well go lithium so have way more usable ah for the same size battery.

[AstroWill]

I mean every RV up until recently has been using some type of lead acid battery in an external compartment. But that is changing.

If you are going to be using it constantly, Lithium is the way to go for the price per cycle, space consumed and usable output. There are plenty of lists of pros and cons but I think Lithium's time is here, and is the way I'm going from here on out.

100Ah rated AGM is 50Ah usable ~80lbs and takes ~5-6hrs to completely charge from 50%DoD.
100Ah usable lithium is ~25lbs and can be charged a LOT quicker.

[pmou]

This is where my brain starts to turn to mush hahaha. do you have an example of one of those Lithium batteries? like price/size? Do you need a different controller to charge them? I was hoping to just run an isolator from the alternator as well to be able to charge the battery while driving, limiting reliance on strictly solar. Would the raw alternator current be too dirty for a lithium battery? I agree lithium ion is the way to go in theory, but this battery was $40 vs $500-$1000 for what I am seeing for an equivalent lithium battery (50-100ah). I don't see how I can justify almost 10x - 20x the price.

Re: my possible lithium ion source, I worked at a bike shop that sells e-bikes and has to warranty e-bikes batteries. unfortunately they cannot ship them back to the manufacturer as you need a special shipping license to be able to ship lithium ion. so they are stuck paying to dispose of them. i picked one up and tore it down and it was actually just 30 or so 18650 cells in there, with one or two of them undervolting causing the whole array to fail. I was planning to harvest a bunch of these and form them into arrays with a smart controller, it looks like you can buy these all in one online for like a 3s4p array which I think would let you run/charge from 12v.

[pmou]

here's what I found inside minus all the fancy circuitry. you could like also leave it intact with all the smart charging circuits, but then you are restricted on input/output voltage.

i think this was a 36v / 460wh battery in its original application.

[Rod's Trucks]

pmou,
In addition to a pair of old C&D UPS 100AHr batteries ( I keep thinking they will fail soon), this is what I have a pair of ( from a different supplier, but identical units):

https://www.ebay.com/itm/Solar-12V-60AH ... Swg75f8bju

After buying the first one, and being very happy with it, I managed to purchase the second one, less the charger module. They are about 13-14 LBS each.
I use these to run a bunch of amateur radio equipment when out on portable operations.
The terminal voltage is a bit high to charge from the automotive source, but if you do not need it to be done fast, I think it would work, but probably not at idle, and not as fast.
I have not tried it yet, but you still need to go thru the built-in BMS controller, in order to get the maximum life from the pack. If I want/need to charge them from the vehicle supply, I actually go thru a small DC-AC inverter, and then use the supplied charger module. It is a bit clumsy, and a bit less efficient, but it works.
When in the field, I usually have a small Honda EU-1000 generator with me. That runs anything I need, (small electric heater, small microwave, battery charging, outdoor lighting; but not all at the same time) if I plan to be out for more than a couple of days.
Rod J

[pmou]

Thanks for the suggestion Rod -- I like that setup. i think that could work well for me, esp since I could then add more later without a lot of difficulty if I decided to add more accessories.

I was looking at something like this: https://www.ebay.com/itm/12V-3S7P-Lithi ... 890.l49292

to re-purpose the cells I might be able to harvest.

or here's a smaller one: https://www.ebay.com/itm/3S-12V-18650-L ... 890.l49292

It seems like this would produce a similar (obviously DIY and limited by my electrical ability, as well as battery health) result to the batteries you suggested.

[AstroWill]

This is where my brain starts to turn to mush hahaha. do you have an example of one of those Lithium batteries? like price/size? Do you need a different controller to charge them? I was hoping to just run an isolator from the alternator as well to be able to charge the battery while driving, limiting reliance on strictly solar. Would the raw alternator current be too dirty for a lithium battery? I agree lithium ion is the way to go in theory, but this battery was $40 vs $500-$1000 for what I am seeing for an equivalent lithium battery (50-100ah). I don't see how I can justify almost 10x - 20x the price.

Re: my possible lithium ion source, I worked at a bike shop that sells e-bikes and has to warranty e-bikes batteries. unfortunately they cannot ship them back to the manufacturer as you need a special shipping license to be able to ship lithium ion. so they are stuck paying to dispose of them. i picked one up and tore it down and it was actually just 30 or so 18650 cells in there, with one or two of them undervolting causing the whole array to fail. I was planning to harvest a bunch of these and form them into arrays with a smart controller, it looks like you can buy these all in one online for like a 3s4p array which I think would let you run/charge from 12v.

I know, it gets kinda complicated. The problem with using more than 50% of your AGM capacity is that you will shorten it's life. I mean you could drain it to 100% capacity every day but it's going to have a very, very short life measured in months instead of years. Really it likes to be discharged the least amount possible to provide the most cycles :)
Plus it takes a LONG time to charge to 100%, and if you don't charge to 100% every single day it slowly damages the battery and reduces the capacity even more.
Take a look at the Lifeline AGM Technical manual, it's a great resource even if for just a general overview.

Charge Time = [(DOD/100) x Rated Capacity (Ah) ÷ Output of Charger (Amps)] + Absorb Time.
100Ah battery at 40% DOD with a 25A charger would take: [(40/100) x 100 ÷ 25] + 3 = 4.6 hours to reach full charge.
10A charger: [(40/100) x 100 ÷ 10] + 3 = 7 hours to reach full charge.
But if you can keep getting them at $40 a pop...very tempting indeed.
Usage does make a huge difference as well, if you are only using 20% capacity twice a month VS cycling them 40% 365 days a year.

I have one of these https://amzn.to/3cbRGda 100Ah usable capacity, small, light, doesn't need venting, won't be damaged if not charged to 100% every day. I would actually like to install this one https://amzn.to/36ckYF0 but with the 100Ah I can easily swap it into my Tiger for testing. It will be a few years until I will know about the longevity of this particular battery.

Being able to use your own cells and your own BMS would allow unique mounting options. Definitely something I'm looking at for the future.