sinbad avatar image

BYD batteries losing charge?

Hey all

So over the last couple of nights, my BYD B-Box 10.24kwh has started losing charge overnight.

A view over the last 7 days clearly shows this.

Victron 48/5000/70-100, running with a CCGX and a SmartSolar MPPT. ESS is running in Optimised mode with BatteryLife, Min SOC at the moment is 70% (Last night it was 65%)

Also noticed that I put nearly 7kwh of solar into the battery today for only a 29% climb in battery SoC.

There's no DC consumers on the system.

Batteries are 3 weeks old now.

Is this normal behaviour or do I have a possibly faulty battery/bms?


BMSBYDdischarge level
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2 Answers
byd-service avatar image
byd-service answered ·

The small decrease in voltage shows that there is a small load. Possibly powering the equipment? That small load is not detected so after 3 weeks probably the SOC needs calibration. I have seen that you have not fully charged the battery in a few days. Can you make sure the batteries reaches 55.2v so it can calibrate (It will calibrate at 100% when the CCL changes to 0)?

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Strangely the behaviour stopped at about midnight last night:

In terms of load - I doubt it. There was mains power on the system the entire time - nothing changed from previous nights where the SoC did not change at all.

The drop of 10% in the space of 9 hours equates to about 110W of power draw for that period - I don't think that's likely in terms of powering the inverter and CCGX given that there was mains available?

Note the perfect flat lines from midnight on

I have set the system into "Keep batteries charged" mode for now, will monitor for a while.


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fully charged

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byd-service avatar image
byd-service answered ·

What´s the load?

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Hi, thanks for the response

At this point (and overnight), the load on the batteries is zero, as the ESS has the system set up in "Discharge disabled" state due to minimum SoC being reached, with the battery showing as "idle" and battery current showing as zero, yet voltage steadily decreases.

Ambient temperature has dropped slightly in the last day or two, but nothing major, and the battery temperature seems reasonably consistent:

Are there any other metrics I can pull to assist?


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Dear Sinbad,

It all looks like a case of small load which one of the known issues and normal. You will not have a fully accurate SOC displayed but the system will work correctly. Please refer to the below guide.

OK, thank you for the update! Much appreciated. One other question if I may, I have tried to register the batteries with (South Africa) but they have not responded. Is this the correct contact?


You can get in touch with our colleague Khan in Afriplus to clarify this.

Thanks again :)