NON-JEEP battery question

[ShadowsPapa]

I have used the Walmart deep cycle 120AH batteries in 2 campers now. The one I had in my popup would run the fridge for 3 days. 3A draw, Stirling style compressor. with no issue. Back it up with a solar panel and you can run it indefinitely.

The one I have now is in my Class C. It is backed up with a normal lead acid battery. Between the 2, I can do a 3 day weekend with normal electrical draw and run a 3K pure sine wave inverter for the pellet stove and the Keurig. Full disclosure, I do have a 100W solar panel on the roof but I can assure you that it's not at the optimum angle (it's flat on the roof)

Yeah, people compare to a fridge or compressor rig - this thing draws 4 amps, 24/7. Even if the ambient temperature is 50 degrees, it's going to run (and freeze whatever is inside)
We had to watch $$ so when my wife said she'd buy me a cooler for Christmas last year, we opted for a thermoelectric cooler.
So I have to figure 4 amps at 12-13 volts full time, never shutting off. If it's plugged in 48 hours, it runs 48 hours. A 3 amp fridge will only run part time - maybe 50%? So that's a much smaller draw and then for only half the number of hours. In 48 hours that draws 3 amps for maybe 24 of those hours, would that be correct?
In 48 hours, mine would draw 4 amps for 48 hours.
Then for being used maybe twice a year, just couldn't see the extra cost of a true fridge, plus the size and weight. This thing weighs about like a regular cooler of similar capacity and the size is not much different from a plain cooler of the same capacity.
(can't lug around things like I used to.)

I have what's left of today, and tomorrow, to "do something". I load up things on Thursday and leave before the sun is up on Friday. Thursday will be spent loading the car, getting the tongue weight right (this car has never been on this trailer) and loading up the tools and cleaning supplies, etc.

So, today and Wednesday to do something or change tactics.
The issue is - it's the Des Moines area - everything is a special order, and stuff like this is a week or more out. Battery I might get lucky, but I'll have to drive around and look - can't rely on the web sites. (been burned by that many times - oh, we have 5 - get there and they have zero)
Solar panel - I've not ever seen any in any store at all.

The good thing about getting a battery is that the one I've been using on my alternator test bench is about 15 years old and needs to be replaced so anything I get could serve triple duty - be used on the test bench, run a cooler, run a winch on the trailer, and I'm sure I can think of other things.

This week sucks. Dealing with migraine and extreme dizziness again this week - damn doctors - only practicing, and keep saying "well if this doesn't work I don't know what else we can do" and they drop it. Medicine in Iowa - ask my wife how many years - decades - they had her on worthless heart meds that did NOTHING until she ended up taking the advice of a neighbor and calling a doctor directly (after having been in Cleveland hosp for a day) Doc last week told me "no don't take this, it will make things worse" after showing him what another doctor prescribed.

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[ShadowsPapa]

Stopped at one of the better Walmarts around - battery selection almost non-existent. Only two "marine/deep cycle" batteries, nothing even close in capacity.

 

[BearFootSam]

Here is how I understand it.
A 100 amp/hr deep cycle battery will run a 4 Amp load a max of 25 hours.
Remember, your cooler will not likely run 100% of the time.
Deep cycle batteries can be drained all the way buy I try and use no more than 80% of their capacity (they say they last longer that way).
I have a deep cycle battery in my fishing shack/cargo conversion camping trailer and carry a generator for the a/c at night while sleeping so I end up charging the battery each night.

Your understanding would be correct with a lithium battery but not lead acid. Maximum depth of discharge recommended for most lead acid batteries is 70% or so. So if the rated capacity is 100ah then your usable capacity is only 30Ah which stinks given the weight.

Pb batteries are also heavily influenced by design, a starter battery will have less capacity but a higher short duration output whereas the converse is true of a deep cycle. With any battery the rate of draw influences the efficiency, most often the lower the current draw the longer the relative capacity. This is to say if you have 30Ah of usable capacity, you may only get 25Ah if you are pulling at 12amps vs 1amp.

Discharge a lead acid battery too far and you have reduced it's life span immensely. Actual capacity is measured via no load voltage, 11.7v is about the floor with a 12v nominal battery. The shitty thing is that as your voltage drops the current increases so your efficiency declines during use.

For all of these reasons in addition to cold induced capacity loss I strongly prefer a good lithium battery. If your need is 100Ah you can get that from one 20lb lithium or two 50+lb deep cycle RV batteries. The former will last 1,000's of charge deplete cycles while the latter only a few hundred. Over the lifespan of the battery the lithium nets an overall cost savings.

Other favorable features of the lithium battery are relatively constant votlage output during drain, (on the better ones) integrated protection and cell balancing circuitry, bluetooth voltage and current output, more robust overall design (tolerant of vibration and temperature).

 

[kb5zcr]

I totally believe you. I've never paid much attention to how often I've discharged my boat trolling motor battery.
Between me and my buddy we've ran it down to almost completely dead many times (certainly less than 200 I'd guess, thats a lot of fishing trips) and its always taken a charge. I do end up having to buy a new battery every 4-5 years ($150 or so).
Also, I had a friend that worked at a golf course years ago and they would run those golf cart batteries down awfully low, he said they replaced them when they wouldn't last for 18 holes (usually several years). Sometimes he would give me two batteries ( they were 6 volt) and Ide put them in my boat wired in series.

I think what I'm running into is I run them below their recommended state of discharge, but by the time I notice anything wrong, I've been using it for five years and a just go buy a new deep cell battery.
I seem to end up needing a new truck battery every 4-5 year too but it never gets totally discharged.

 

[ShadowsPapa]

Jim is right, describing well the actions of the different battery types.
AGM do better than traditional wet cell lead-acid batteries, but still if you drop them below a certain point, and do it often enough, you lost capacity. They will no longer give you 100% of what they did when new even from a "full charge".
Lithium batteries you can think of more like your phone or tablet or laptop - you can run them down below 10% and do no long term damage as far as capacity drop. They will naturally with age get to the point they won't have the stamina or long life (a slight reduction on hours they'll run your tablet or phone).

Lead acid batteries all have a self-discharge issue - AGM not as bad, but it's still there.
Charge it to 100% and set it on a shelf, not connected to anything, and it will drop.
AGM is anywhere from 1 to 3% per month. So one that's 100% charged October 1st with nothing at all connected can drop 3%. Add to that any parasitic drain at all, an electronic radio put in your 1970 Camaro, for example - where one lead is ignition connection and the other is battery connection, now you drop that 3% plus whatever that radio takes in.
That's all at a specific temperature - self-discharge is lower at colder temperatures and much higher at temps in the 90s so your battery this year in Texas is self-discharging a possible 50% faster -say a drop of 4.5% per month just sitting disconnected from anything.

"Standard" flooded cell lead acid batteries can self-discharge up to around the 8% area per month. So letting a classic car with a stereo installed sit for a month means you've likely dropped it enough you could be doing damage.

It's one reason for AGM batteries in solar arrays and modern cars. Lower rate of self-discharge.

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