Slow charging for my B300 battery

I have just purchased a refurbished B300 battery on the official bluetti store on eBay France (solarenergie-eu).

Compared to my 4 new B300 batteries purchased last year on the Bluetti website it does not charge in the same way.

With a maximum load: 16 A and 230V, 3000W silent mode disabled on my AC 300 and one battery connected :

My previous B300 charge at 3 kW up to 97-98% and then this reduces for the end of charging; normal operation for me.

With my refurbished B300 battery:

  • starts slowly (200 W to 500 W for a few minutes) from 0% to 3%

  • 3000 W up to approximately 50%

  • 2500 W at 55%

  • 1500W at 65% / 70%

  • slow end of charge (600W) past 90% or even very slow at the end.

The BMS limits the charge more quickly; I tested with 2 AC 300 and by adding 500W via a T500 charger directly to the battery the load drops by 500 W which proves that it is indeed the BMS which reduces the incoming load.

On the other hand, no problem in discharge: I drained fully (3 kW) from 100% to 80% without problem and the capacity test is correct: 2650 Wh obtained in 4h30 hours with a resistive load. Given the self-consumption of the AC 300 in 4h30 and the announced efficiency this seems normal to me.

The only difference is that my refurbished B300 battery has the latest firmware (1021.7) not the others (I haven’t updated them yet)

In practice this operation will have little impact because I do not intend to push the equipment to the limit on a daily basis; but I fear that the BMS will limit the charge because the battery is well worn out. I’m still within the free return period for EBay so I’m wondering.

If a Bluetti administrator can ask for the opinion of a technician if it’s normal or not that would be cool :) Or if the new firmware is different (more careful about charging). Or a bug.

Battery serial number: 17.0301.0946-01A1

Firmware : 1021.7

My 2 AC 300 have the latest firmware.

Thanks in advance

Hi @ThierryFr

even you say this B300 is different from you others, i wouldnt say that this is a bad or wrong behavior. Its normal that batteries start slow to charge, charge faster until they reached a “sweet spot” and to the end, they become slower again.

You metioned a newer BMS firmware version of the refurbished one. Maybe this update was published to guarantee a longer lifetime of the battery with this kind of charging curve.

So as i said, see nothing wrong with it. Im sure when you update the B300s firmware on the other units, you will see the same effect.


@Selfmadestrom BMS updates generally improve management strategies. If there are no problems during use, not updating will not cause problems.

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Thanks for clarification!