Small Cabin

The battery does not use battery power to heat the battery.

You should be able to get any LifePo4 battery in any size you want, not sure why you think you can only get Relion. Even amazon has a wide selection these days, but there are lots of options out there.

The thing with lead is you really shouldn't drain them past 50% capacity, and not even that often, LifePo4 can easily run down to 20% capacity so you get more power out of them, but they come with issues that cold weather causes. Basically if you want to charge them, they need to be above freezing.

You numbers look reasonable, batteries almost charged so amps being put into them is low, just topping them up. But since we don't know your parameters of your charge controller its hard to know. If your using the preset lead acid charge level on Epevers, its only going to charge to 13.8v, so your almost there.

Suggest you do some research before you make a change. I could type novels on the subject, but its already on the internet so do some research. DIY solar forum has very good beginner info.

I'm surprised your old batteries lasted given that what you have for solar likely never managed to do an Equalizing Charge as it is grossly under capacity to do so... It's unlikely they ever really hit a full charge & got equalized, which likely killed 1/2 their lifecycle right off the bat.

In order to make suggestions/recomendations, would need more details on the gear you have in place, what you are using now and plan on over the next few years. I'm up near Algonquin Park so I know what your dealing with pretty much with regards to our weather & sunhours.

Unfortunately, you picked a terrible time in the year to start furtling around with your solar system.

First, have you done an ampacity calculation on your wires. You say the panel is 100' away. I'm guessing that means 100' away from the solar controller? So you are pushing 47V with a max amps of about 8 over 100'. A quick calculation says you would need 8AWG with a 3% loss. 10AWG would have a 5% loss!

For FLA, the secret is having enough capacity. More=better for longevity. As others have said, not pulling below 50% is crucial. However the higher you can keep the state of charge (SOC), the longer FLA will live. If you are going to keep FLA, then I suggest you double the batts (4 6 volt).

As to corrosion. Ensure you are using some sort of anti corrosion paste (some people just use vaseline). Second, you have to ensure things are super clean before you make the connections. Finally, ensure your connections are tight. You need to check them about once a month and re-tighten as necessary.

Another suggestion would be to ditch the Epever controller. While they work, they are not the best, especially in shady or cloudy environments. Victron are cheap enough now. With that being said, I would prioritize the batteries before replacing the controller.

use a large enough gauge AWG cable (not solid wire) in

Another suggestion would be to ditch the Epever controller. While they work, they are not the best, especially in shady or cloudy environments. Victron are cheap enough now. With

Well I ordered a Victron 100/50, due here today. Going to miss the Epever, especially the MT50 readout staring at me. With the Victron I check things by looking at Bluetooth?

You Need to use a large enough gauge AWG cable (not solid wire) in copper, not alum to avoid more than the prev mentioned 3% line loss to the solar charge controller.
The scc Needs to be close to the battery bank and the inverter close to the bats all connected with adequate awg cable for the max load.

The inverter has its own fuses so you dont have to run it into a fuse box (for a larger system you should). Once the dc has been inverted to ac you can run a pretty far distance to your devices within the cabin with no more than std 'house wiring' (though with a small place even extension cords can be ok).

ALL connections Need to be solid, clean and proper.
You lighting is LED bulbs, they, and usb chargers etc draw so little that you almost dont even need to add the draw up. The inverter also has a draw when on even if it isn't powering anything. A 300w is likely about 85% efficient and a pretty low draw but turn it off when you aren't using any power to save energy.
If this is basically all you are powering 100ah of bat-bank should be plenty, even with lead acid bats. Because you say you get a 'bat low chime' from the controller that doesnt sound right. Are you sure you have the scc wired correctly to to bat bank? IE, the big wires to +/- (not the 'load' tap on the scc).

I would expect the chime would maybe come from the inverter shutting down (Low Voltage) because you had a failing bat in the bank as the bad bat pulls the good one down and chokes your output.
That is just what happened to me a few years back as the old set of 4x100+ah bats were dying off one by one. We limped through that last season and I had to decide buy more LA bats like you or change to LFP; we went (unheated) LFP but are not in your far north zone and hardly use the cabin in the winter (my aio portable is power when we do).
Fwiw, if I were you, Id make sure things are set up as good as possible as you are but learn more about this 'solar/bat electric thing' and do it way better on the new build.

Based on your last post, it seems that you don't have enough solar and batteries. If you are getting alarms for low batteries, that is not good. However, something is henky here. Your 2 Trojan 6V batteries have 2700 Watt hours(WH), divide by half and that is 1350WH. There is no way those lights, phones, batteries should use that much power. As an example a Ryobi 4AH battery has a capacity of 72WH, with losses that about 100Wh. Even if you charged 4 with no solar that would only take 400 of the 1350! Phones are like 20WH MAX.

I’ll see how much trouble to keep the Epever there for easy switch to see the difference on same day.

I want to say the wire is 8 or 10 gauge. I know it's significantly thicker than standard household wiring. It's definitely copper, I've never even seen aluminum wire. The line from the battery to the scc is about 36". All the connectors are quite heavy gauge.