SOC Bluetti Batterie

Common question on this group: “Why does my Bluetti solar generator seem to have lost autonomy or seem to display anything? And what should I do in this case?”

Bluetti solar generator batteries are all based on lithium-based chemistries (lithium-ion or lithium ferro-phosphate).

To effectively use this type of generator, whether from Bluetti or another brand, it is better to understand how it works and the specificities of lithium-based batteries.

Each battery is connected to a management circuit (the BMS: “Battery Management System”) which takes care of regulating the amount of energy that it takes or sends to it.

Of course, to make its decisions, the BMS must constantly know the state of charge of the battery (the SoC: “State of Charge”).

This is given by the voltage across the terminals. For “classic” lead-based chemistries, it is very easy to obtain an accurate value of the state of charge because the difference between a 48V battery charged between 20% and 80% is 6V, since the discharge with lead is linear.

On the other hand, for lithium-based chemistries, for a 48V battery, this difference, for the same range, is only 0.5V, because the discharge is not linear. This is even more obvious for lithium ferro-phosphate than for lithium-ion.

It is therefore very complicated for the BMS to know the precise state of charge of a lithium-based battery. Manufacturers must therefore find ways to refine the state of charge value, such as a charge/discharge statistical system to weight the charge values ​​read by the BMS.

Added to all this is the fact that the batteries of solar power plants are made up of several smaller sub-batteries (the cells), and that these do not charge/discharge in a homogeneous way depending on the context of use. use, their wear, and a number of other parameters.

When a battery has cells with unbalanced charges, it has less energy than it seems, and this is true for all chemistries.

The consequence of all this is that after a certain time of use, a generator comprising a lithium-based battery begins to behave strangely, until it suddenly cuts out, or displays totally fanciful remaining autonomy.

This is not a malfunction, breakdown, or permanent loss of battery life, but a normal phenomenon, which can be corrected by a so-called “SOC” procedure.

This will rebalance the cells and return clear voltage values ​​to the BMS to restore the entire battery to an optimal state, and therefore correct all these bizarre behaviors.

This “SOC” procedure can be carried out as a preventive measure or as a corrective one, but as it consumes up to three charge/discharge cycles, it is better to do it only as a corrective one.

For example, when the solar generator is new, just charge the battery to 100% and start using it, since it has, by definition, not had any usage time which could have caused the BMS to drift .

To perform the “SOC”, simply proceed as follows:

  • Charge the battery to 100%, if the BMS allows it, otherwise, charge it to the maximum that the BMS allows. Do not connect anything that could consume electrical current, which would distort the procedure.

  • Once the battery is charged to 100% (or to the maximum that the BMS allows), it must be discharged until the extinction of the generator (0%).

    It is possible, in the event of a large drift or large imbalance, that the battery provides energy for a long time despite a display of 1% remaining.

    As soon as the generator is switched off when the battery is in deep discharge, you must start recharging it as soon as possible or risk damage, especially if it has a lithium ferro-phosphate (LFP) chemistry. However, if the battery is hot, the BMS will refuse to start the charge, it will then be necessary to wait between 40 minutes and 2 hours before being able to recharge it again.

    If you are not in a rush, prefer slow or moderate charging power. Recharge to 100% in one go, if possible.

If the problems are corrected, you can settle for a single charge/discharge/recharge cycle. However, for certain reasons, in particular related to the operation of the BMS, a “SOC” procedure is only really optimal when at least 3 cycles have been executed.


@BLUETTI Maybe this can be add to some FAQ or something?

Seems like pretty detailed


@Jeff_bzh Hi Jeff,
Thank you for your feedback and comments. I’ll go ahead and forward your post to the tech department so they can take a look at it first.
I will message you again once the team has a response.


My comment is correct ? I don’t understand What you mean

@Jeff_bzh Yes. The SOC acquisition accuracy is not perfect, there may be a little error.
With the extension of the system use time, the error of SOC may also get bigger and bigger, then you need to do a sub-power self-learning: discharge to 0%, then fully charged, re-calibrate the SOC to 0% and 100% voltage, re-calibrate the SOC.

Oui, l’exactitude de l’acquisition SOC n’est pas parfaite, il peut y avoir une petite erreur. Avec l’extension du temps d’utilisation du système, l’erreur de SOC peut également devenir de plus en plus importante, alors vous devez effectuer un auto-apprentissage de sous-puissance: décharger jusqu’à 0%, puis charger complètement, recalibrer le SOC à 0% et 100% de tension, recalibrer le SOC.

Hello @bluetti , that’s what i was explaining :wink:

1 Like

I have an AC200p, and lately, there’s a problem with capacity. I tried constant discharging/recharging to reset the smart shunt to display correct capacity, but I believe that’s not the problem either. When fully charged, each cell display 3.30volts, 56.8V pack voltage(should be 52.8V?) The unit was able to recharge under 2 hours(only 1.1Kw entered) The 2,000Wh battery somehow can only fully charge to only half its normal capacity. Constant discharging yielded about 880 watts( less than half capacity). Any suggestions?
Thank you.
Linh P.

did you leave it for a long time with a 0 charge?