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3dclassen avatar image
3dclassen asked

Smart Lithium - 200Ah - Shows low voltage of 4,8v (SOC was 40%) - Bluetooth not working

Can´t find an appropriate answer, so I am starting this thread:

I have a VICTRON Smart Lithium Battery (200Ah) which worked all fine for 2 years now. With the cold in Germany the Charging was disconnected and after a while also the Load. All good. The SOC was 40,7% the Voltage 12,07V at this point.

I decided to put the battery in a warm storage, while being so cold, for charging externally. After 2 days of "warming to room temperature" I decided to charge the battery with a car charger. At this time the battery shows 4,8V and Bluetooth isn´t working anymore.

Is anybody aware of this problem?
Is this some kind of "conservation mode"?

Help is pretty much appreciated, as I need the battery in the next days!!!

Thanks in advance...Daniel

Lithium Battery
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1 Answer
Stefanie (Victron Energy Staff) avatar image
Stefanie (Victron Energy Staff) answered ·

Hi @3dclassen

There is plenty to say about this, though most of it is covered in the manual and even more here in the community (try the search feature).

  1. If the battery was at 12.07V (which translates into a cell voltage of roughly 3.02V), this is nowhere near 40% SoC. It's more like 3-5% max., which is not enough to put the battery to storage because it's almost completely discharged. Wonder where the 40.7% is coming from. The SoC is by no means suitable for displaying the actual condition of a battery. Cold temperatures lead to a significantly lower battery capacity than the battery monitor calculates, the smallest discharge currents cannot be included in the SoC calculation etc.
  2. Bluetooth stops working below 8V. See the manual.
  3. 4.8V means less than 2.5V for a single cell. I'm afraid that one or more cells are permanently damaged.
  4. There is a recovery procedure described in the manual which could help bring the battery back to life. No guarantee and be careful to follow the guide step by step and under supervision. Don't even try if you don't know exactly what is required!
  5. Even if you're lucky enough to get the battery back to life, it still must be considered dangerous to use it as if nothing happened.


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3dclassen avatar image 3dclassen commented ·

Hi @Stefanie (Victron Energy Staff),

many thanks for your answer...though it´s bad news :(

I am aware that the SoC isn´t showing the health of the battery, that´s for sure. To clarifiy the situation:
The battery worked fine for more than a year. Last voltage was 12,07V on 18.02.2023 (= 40% SoC). I have all monitored in VRM.
Due to the cold temperature I put the battery in a warmer place, for charging later. Five days later with no use or charging the voltage showed 4,8V. I am wondering that the voltage can drop this significantly in 5 days. But I am not an expert.

To be honest it´s also a problem for me to charge the battery when it´s so cold outside, because the BMS stops charging below 5°.

If I may ask, I would have two more questions, which I would be more than happy to get an answer from you:

  1. Can I try to charge the battery with shore power in my system with BMS and if this is not working, trying your method with opening up?
  2. If the battery comes back to life, how can I monitor if the battery is damaged?

Again, I am more than happy for your answer, thanks!
Cheers, Daniel

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Stefanie (Victron Energy Staff) avatar image Stefanie (Victron Energy Staff) ♦♦ 3dclassen commented ·

I can't comment much on the voltage drop within 5 days. It happened for a reason. It's definitely worth to study the manual from top to bottom, especially the Discharging chapter, which will give you a rough idea what and why it happened.

Again, a battery voltage of 12.07V means not much left in the battery, almost completely discharged, and while in the "knee" of the discharge curve, the voltage drops even faster. Depending on the discharge current this can happen in seconds. That's why you must take extra care and don't let the battery get that far discharged. The BMS is only a last resort. And when it kicks in for whatever reason, immediate action is required to recharge the battery before it discharges even further right into the "no go" zone.

Yes, charging the lithium below 5°C requires additional effort.

To answer your questions:

  1. No, don't even attempt to do that. Isolate the battery from the rest of the system and follow the Charge procedure for recovery after low voltage event step by step. You need a charger where you can set the charge current to as low as 0.1A until the voltage of the lowest cell increases above 2.5V. Opening the battery is not that difficult.
  2. You can attempt a full charge and discharge cycle (all under constant supervision!) and see how much Wh you get out of it. But even then I would consider it unsafe to continue using the battery.
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3dclassen avatar image 3dclassen commented ·

Ok, Understood. Thank you very much for your fast reply.
One last question: Why is it unsafe to use the battery, because of the capacity-drop or any other, more severe reasons like heat development or other critical conditions like burning?

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Stefanie (Victron Energy Staff) avatar image Stefanie (Victron Energy Staff) ♦♦ 3dclassen commented ·

Not because of the capacity-drop but heat development, bulging etc. Something that is completely out of control. Can you sleep soundly knowing that something is no longer 100% safe? I don't.

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