Need to upgrade my Batteries and inverter... Any point in switching to AGM or LIPO?

Elfmaze

Observer
Hey guys, My batteries are coming up on two years old and i'm starting to have some low voltage alarms on my cheap walmart inverter. I'm not sure if its the inverter or the batteries, but I'm guessing the inverter is set to have lo battery way to high to protect starting batteries in a civic.

Power system consists of:
2 X 100 watt of Renogy solar panels
2 X 105ah Walmart Deep cycle batteries
Renogy 30amp PWM LCD charge controller

It runs a vent fan, tv, led lighting and cell phone chargers. The TV is where we have been having issues lately. worked great for the first year and a half.

I have been looking at some different inverters. I would love to get a nice Sine wave 1500 watt range inverter. was looking at something like a go power 1500 watt sine wave inverter.

But the battery issue... The Walmart Cells cost me $100 a piece. I see people dropping hundreds more if not thousands more for the Lipo cells... Is there a reason? I understand the lipos will be more stable and drain deeper but I can replace the Walmart cells ten times over for the same cost and recycle the old ones. What am I missing?

Any recommendations are welcomed!
 

mikekey

Deplorable
But the battery issue... The Walmart Cells cost me $100 a piece. I see people dropping hundreds more if not thousands more for the Lipo cells... Is there a reason? I understand the lipos will be more stable and drain deeper but I can replace the Walmart cells ten times over for the same cost and recycle the old ones. What am I missing?
I wouldn't go with lithiums for your setup. I have 400aH's of lithiums onboard my Airstream. But I live out of it.

For me the advantages are that the batteries accept a full rate of charge until fully charged. If you can throw the power at them, you can recharge them really really fast. I have a 100amp charger, and can recharge in under an hour with the generator if needed. But my 805 watts of solar handles it most days.

Also I could use 80%-90% of the capacity of this bank. Which means we could have between 320-380Ah of available power. I would need six 6V batteries to get the same amount of amp hours. So if you have a 12v battery with 100aH at 50% discharge it's only 50aH where 100aH of lithium is actually 90aH.

The charge/discharge curve of lithiums is very flat. It's impossible to tell current state of charge by battery voltage alone. During discharge, the voltage will vary about 1/10 of a volt. So voltage tells you one of three things; the battery bank is fully charged, dead, or somewhere in the middle. This is the complete opposite of lead acid and AGM batteries were the voltage drops as the battery is depleted. This is a bonus for getting maximum power out of the bank all the way to the end. it's also a bonus for running a bunch of stuff or something like a winch where you want a constant voltage.

You're right that Walmarts are cheap, but performance wise, they'll never be the same or even in the same ballpark. The thing is lithiums aren't apples to apples with lead acid. They're actually apples to oranges becuase of all the differences in the systems.

 

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Elfmaze

Observer
I also see costco has some 6v golf cart batteries. As I currently understand I divide the 20hr amp hour rating to compare the batteries?

Now the interesting thing about the golf cart batteries is I think I could fit four of them in my battery compartment since I have height on my tray. wired series vs parallel but otherwise I probably wouldn't notice any difference? Figure the golf cart batteries are build to take a bounce too.


 

thedavidzoo

New member
Mike,
I'm in the process of putting together a 400Ah lithium bank with 640W (4x160W, 12V) solar and 1500W inverter. Originally we were going to use 4 6V and a Morningstar MPPT 60...easy, but don't really have the space and HATE the weight! I am having a hard time finding info on solar charging of the lithiums with the sizes/capacities involved. Could supposedly still use the MS MPPT on custom setting, but read something about not working with BMS.
Can you give me the specs on your system? And maybe where you acquired the parts?
Sorry for the hijack...
 

4x4junkie

Explorer
Mikekey covered the advantages of lithium (LiFePo4) well, though if I'm not mistaken, their performance tends to suffer more in cold temperatures than does lead-acid. LiFePo4 batteries also have 2-3× the energy density of lead-acid, meaning a 200Ah LiFePo4 battery bank will be about 1/3 - 1/2 the size & weight of a 200Ah lead bank (1/6 - 1/4 the size & weight if you factor in the 50% rule and compare to 400Ah of lead batteries).

The advantages of AGM over flooded however are far less dramatic. AGM batteries do have very slightly better current capability, both in discharging and charging, however unless you're using a single small battery for both starting/winching and deep-cycle service, this difference is not of much significance (and essentially becomes non-existent if you have a dual-battery setup). Energy density between AGM & flooded is basically identical.

I agree, given the relatively light usage on your setup I see no reason to spend big $$$ on LiFePo4 if there isn't also a big concern over the weight of the batteries.
 

Joe917

Explorer
Mikekey covered the advantages of lithium (LiFePo4) well, though if I'm not mistaken, their performance tends to suffer more in cold temperatures than does lead-acid. LiFePo4 batteries also have 2-3× the energy density of lead-acid, meaning a 200Ah LiFePo4 battery bank will be about 1/3 - 1/2 the size & weight of a 200Ah lead bank (1/6 - 1/4 the size & weight if you factor in the 50% rule and compare to 400Ah of lead batteries).

The advantages of AGM over flooded however are far less dramatic. AGM batteries do have very slightly better current capability, both in discharging and charging, however unless you're using a single small battery for both starting/winching and deep-cycle service, this difference is not of much significance (and essentially becomes non-existent if you have a dual-battery setup). Energy density between AGM & flooded is basically identical.

I agree, given the relatively light usage on your setup I see no reason to spend big $$$ on LiFePo4 if there isn't also a big concern over the weight of the batteries.
X2. Adding a battery monitor such as a Trimetric would show you exactly what is going on in your charging system. The most useful tool for extending battery life.
Are the Walmart batteries flooded, if so have you equalized them recently?
 

jkam

nomadic man
That looks like a pretty big battery box.

If you could stack 4 6V Trojan T 105's in there, you would have ample power to do just about anything. It would be way more than you need
for your current usage. It would allow you to start using more power if you wanted in the future, so nice to have.
However, they weight about 68 lbs. each so are heavy when 4 put together. If you can carry the load, I would do that.

The T 105's are a proven performer for many years, are much less expensive than either AGM or lithium.
Put a watering system on it and check every so often and they will give you many years of service.

I just replaced my over 8 year old T 105's in my RV. I have two and while I'd like to have two more, I have nowhere to put them.
This is only the 3rd set of batteries in 20 years on this RV, all using T 105's.
I paid about $160 each for them, but it is worth the little extra you spend in years of service if maintained well.

Oh, and I'd upgrade your charge controller to an MPPT one, it has made a difference on my system which is using two 80 watt panels and a Morningstar MPPT 15.
And get a better inverter, I use the Xantrex Prowatt SW 2000, it works great for me off the grid, I just plug my shore power into it and it allows me to use all the
110 outlets in the RV. I leave it on all the time and my solar system and batteries do fine keeping up with my usage.
 
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luthj

Engineer In Residence
I have 3 suggestions (mentioned above by others).

1: Get a battery monitor. Xantrex and Victron make good compact units. Trimetric works, but is a bit hard to mount, and is not as adjustable.
2: Go with true deep cycle batteries. The cheapest way to do this is with Golf Cart style Flooded units. 4x GC2 or similar will get you over 400AH in a series parallel configuration. These types of batteries are designed for deep cycling and vibration and will last much longer than walmart batteries. Costco GC2 batteries will run around 100$ each.
3. Make sure your solar charger is getting to a high enough voltage during the absorb phase. Too low of voltage won't fully charge the batteries. The easiest way to ruin a lead acid battery is to chronically undercharge it. The second is to cycle it below %20 SOC regularly. (50% for normal days is recommended). Flooded GC2 batteries often like too see 14.6-14.8V During the Absorb phase.

The battery monitor (must have a shunt!) will tell you how deep your batteries are getting discharged, and if they are getting a fully charge. With your usage a 200-300AH bank should work fine. So 2x GC2 batteries will work. Could also go more if you have the payload and space available.
 
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