Is it normal for two of these batteries to become ‘lopsided’ while charging/discharging? I charged them both up to 100% but within a week of daily use I saw one at 29% while the other was at 50%.
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What happens if one goes down to 0% while the other is say, 30%? Is there some kind of built in protection to keep one battery from being totally discharged (while the other battery still has power)?
This is not an uncommon issue on the B300 batteries. This thread talks about the issue a good deal AC300 - Different BMS on B300 and different discharging rates - #11 by BLUETTI
I have an AC300 with 2 B300 batteries. I have drained them all the way to zero to calibrate the SOC and when the lower of the two gets closer to 0% the AC300 draws more power (seemingly) from the battery with the higher SOC. So far other than being annoying, it hasn’t been a problem. My only two cents is to keep an eye on it. Don’t leave it unattended for extended periods of time when there is a constant load on it. Some users on the forum have reported their B300 battery getting discharged to extremely that they couldn’t revive it and had to return it to Bluetti for a replacement.
@St8kout Are both B300S connected to the AC500, or one by one in series? Please connect both batteries to the AC500.
Is your Bms version up to date? You can fill the batteries separately and connect them together again to see.
Yeah, each are plugged into the AC500. No updates are pending.
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The trick seems to be they have to be recharged to 100% to “reset” the imbalance back to equal charge/discharge percentage.
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When I first noticed this we had 4 days of clouds and rain, so the batteries only got recharged to about 90% when the sun peeked through. So without getting to 100% charge the imbalance kept growing day by day. It has to get to 100% to reset them to be equal.
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Maybe all it needs is a line of firmware code to monitor the imbalance (and make corrections if needed.)
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I am also having this same issue my one of my b300s was at 80% and the other completely died and shut off this needs to be fixed this system was not cheap
Is this problem fixed for you? I am getting my second battery today and am a bit worried now. @BLUETTI stated that I don’t have to worry about the different SOC of each battery, but reading this thread looks like there are imbalances…
There’s always some imbalance between my 2 batteries, but it ‘resets’ when they both get to 100%, which is every morning.
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The software that displays the SOC is a bit slow so when you first open that page on the app it can show a large difference, but give it several seconds and it will show maybe a difference of around 3 to 6 as they dischage and recharge.
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I’m using PV Priority without plugging it in to a wall outlet, with SoC setting of 10% (it doesn’t get that low but I don’t want it shutting down since it’s powering my fridge.) Except for the house lights I’m pretty much running off-grid 24/7. NVEnergy shows our daily power usage (because our meters are wifi connected to them). It shows the average for my last bill was $0.89 per day. It’s kind of fun to see how low I can get it. 
The battery imbalance issue is annoying at best and problematic at worst. I keep an eye on my batteries (B300). When emailing Bluetti about this issue, their response was that they have no plan to address the issue. I have it in an email and can’t remember the exact words.
Mine seems to be evening out on it’s own from daily use. By the time the sun comes up it can be as low as 22%. Then by 11pm both batteries will be topped off at 100%.
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Even now that the sun has gone down, both are at exactly 76% discharge state.
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When you first open the app to Battery Info, give it maybe 10 seconds. Sometimes when I first look at it they can be wildly different, say one battery will read 100% while the other 80%, but after several seconds the REAL readings come up and lately there hasn’t been much of a difference, maybe 2% difference.
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As I’ve said before, getting them to 100% seems to reset any % difference.
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I was reading up on LifePo4 battery charging. Apple seems to be the experts on this. There is actually no direct way to measure the SOC. Apple says what they mostly track is time of use or power cycling. On my Macbook Air my usage habits are noted and for daily use, the batteries are programmed to stay at 80%. If I unplug it on certain days, the programming will charge it up to 100% the night before.
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But anyway, the point is that you can’t determine the SoC from voltage or current readings. It’s likely a programmed educated guess by how much power goes out and comes in, and time of usage. They can likely only tell when it’s close to 100% (because charging seems to slow down.)
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I wouldn’t sweat it for now. As I said, mine seems to be evening out from daily use of maybe 4 weeks now.
I just added a 3rd B300s and it threw off the SOC numbers as when I added the 2nd Battery, but I expect it will correct itself just like it did before. I charged it to 100% by itself before re-connecting the other batteries.
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The extra backup power is great, as now I don’t have to worry about fully discharging them at night. They are, however taking a really long time to get back to 100%, (kind of expected that). Two batteries would be fully charged by 10:30am. With three, at 1:12 pm they are at 93%. 