Battery help please

I have a question I hope someone can help me with.
First the system I am building in case it matters:

0MPPT Solar Charge Controller Epever 12V/24V MPPT Battery Regulator 150V Charger
Giandel 4000w Heavy Duty Pure Sine Wave Power Inverter DC24v to AC120v
10 x 100 watt Renogy monocrystalline solar panels

I bought 2 batteries off Amazon: Shunbin 300 amp - 12 volt (I know they aren't the best choice but I simply can't afford battleborns)
This is where the question arises
I want to do a 24 volt system which requires me to connect the 2 Shunbin batteries in series.
Before I connect them in series it seems I need to balance them.
Every time I try and find information on this I keep finding info on how to balance cells, not batteries. It's a nightmare to just get this little tidbit of information figured out. I read threads, watch videos etc and more cells info, never batteries...
I connected the 2 batteries in Parallel to see if they would balance each other, and after around a week connected one is still reading 13.4 volts on it's display and the other reading 13.2 volts.
I don't want to damage anything, and I have spent too many failed hours searching for the answer to what I need to do, so I am finally making an account here to ask for help. I am noob, total noob, so any simplified help/advice would be appreciated a great deal.

Hi Rusty,
Not sure, if my advice will be any help, but here it goes:
Balancing is quite an important part for cells in a battery as Lithium based cells are somewhat sensitive towards overcharging etc. Hence each Lithium based battery needs a BMS (battery management system). Now your Shunbin batteries most probably already have one built in (the one that shows you the 13.2 and 13.4 volts respectively). So that takes care of the individual cells. For your batteries, they are balanced if you connected them in parallel (for which I always would recommend to use a high-power resistor of 1 Ohms or so just to limit maximum current to not damage too far off batteries).

So long story short, if you already connected your batteries in parallel and still have 0.2 volts different, then this is most probably the reading error of the BMS! Just make sure, your Shunbin batteries allow for series connection (not sure, but I heard, some BMS are not recommended for series connection).

Rusty1234 said:

still reading 13.4 volts on it's display and the other reading 13.2 volts.

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Its quite possible the readings on the built in meter is incorrect, have you verified the voltage with a meter at the battery terminals?
There are reports on this forum and from other sources that the batteries from Shunbin have reliability problems and are built with used or rejected cells. ( a search will find).
When connecting in series its possible, with mismatch in the BMS and cell performance in each battery, that issues may arise during charging and discharging.

The preferred option would be to return the batteries for a refund. ( or sell on Ebay)

If returning the batteries for a refund is not possible, then charging each as a 12v battery to full,14.6 volts at the terminals, ( or alternatively discharging to a low value, 12.0 volts at the terminals) before connecting in series could be something to try.

A further option would be to break down and rebuild the batteries as 24 volt batteries, each with a replacement 24 volt BMS. The rebuild could use the same case.

Hopefully members with experience using these Shunbin batteries will be able to offer further advice.

Mike

Hey thanks a ton guys, I appreciate all the info you have given me!
I did a test of the voltage at the battery terminals and the one display is off by .2
I have read the info on here about Shunbin batteries and it does seem a bit mixed, with some people saying they are garbage but not offering much in the way of an explanation as to why they feel that way, and others saying they used them with no problems other than a bit less wattage than advertised.
For me it was a price thing. I hate gambling but I just can't afford to spend the money that battleborns would cost to get the same amount of watts. (I'm in Canada and a Battleborn is minimum $1200 each here) And I am really not confident in my abilities to build a battery from scratch. It took all my courage to do my own system instead of an iNergy pre-built etc.

Thanks again for the tips!

I suggest you read through this thread. I think it was well explained why they are garbage. Maybe Shubin has improved since then, or maybe some are lucky.

Gazoo said:

I suggest you read through this thread. I think it was well explained why they are garbage. Maybe Shubin has improved since then, or maybe some are lucky.

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Thanks, I just read that whole thread.
Short of Delta-Vs BMS going on him it seems the top complaint is that it isn't as advertised.
If the 2 I bought can give me 5000 watts instead of the advertised 7200 watts it's still a win for me.
To get to 5000 watts with a reputable brand would have cost me double, and I have already pushed my limit financially.
If they don't die completely on me and can give me a good 10 years of power it's a win.
I hope to learn enough here to actually build my own battery banks for when these ones are done, and as mikefitz said I can even use the same boxes.
I am sure in time I will likely regret buying them for one reason or another but my noobness prevents me from seeing the whole picture at the moment.