Briggs and Stratton instart - Battery imbalance repair
Introduction
Go to step 1If the green and red LEDs on the charger flash alternately there is a high probability of a battery imbalance. This usually occurs when the battery has not been charged for a long time and the individual cells have discharged differently. The charger cannot compensate for this imbalance. These instructions describe how the cells can be brought back to the same voltage.
What you need
-
-
Plug the battery into the charger and check if the green and red LEDs on the charger flash alternately. If yes, there is a high probability of a battery imbalance and the following steps might solve the issue
-
-
-
Open the battery by removing all 4 TR10 screws
-
The cover can be removed without much effort
-
-
-
Measure the voltage of all 3 individual battery cells
-
Cell1: BV+ - BV2
-
Cell2: BV2 - BV1
-
Cell3: BV1 - BN
-
If cells have different voltage (>0.1V) this indicates a battery imbalance
-
-
-
Charge each cell to the highest individual cell voltage (no need to fully charge all of them)
-
Set power supply to 4.1V and limit current to 750mA. 750mA is the standard charging current for a LGDAHB21865 cell. If the battery has different cell type, the datasheet needs to be checked first.
-
Important: Do not exceed cell type rated charging voltage or current. Refer datasheet.
-
Connect the power supply to the terminals of the individual cell and charge until terminal voltage reached. Make sure polarity is correct (positive to positive and negative to negative). Observe the charging procedure at all time.
-
Important: Individual cells are not protected against reversed polarity. Wrong polarity will kill the cell.
-
Note: If battery cell is not charging the cell might be dead. Don't continue charging and consider replacing the cells or recycle the battery.
-
At the end of the charging procedure verify each cell has same voltage using the multimeter (+/- 0.01V). Note that cell voltage provided on the power supply unit might not be the same when measured with the multimeter.
-
-
-
Reassemble the battery and charge it using the original charger
-
Battery is charging normally until fully charged
-
Note: If the issue occurs again during the charging process this would mean that the individual cell were charged at different rates. The cells aged differently and the internal resistance is not at a similar level anymore. Only replacing the cells would solve this issue. Consider contacting a re-cell service.
-
Cancel: I did not complete this guide.
One other person completed this guide.
10 Comments
That's cerainly possible since the battery management does not lock the charger after an under discharge event (like some do). Replacement comes with some effort. Here I found a step by step disassembly guide. Challenges I see in finding a specific battery type with similar properties. Replacing the batteries would also require a spot welder. Avoid soldering the batteries to the terminals since the high temperature could permanently damage the cell. Always replace all the cells, not only individual ones.
If you are not firm with the topic consider buying a new one or contact a so called re-cell service.
My battery keeps working so far but in case a cell actually dies I will replace them and create an additional guide for this process.
Good luck and best regards,
Joel
Your solution worked. I charged the cells with two wires from phone charger..., cause it was the only thing ive got:) 5V 0.7A. For now its ok but I fear that the voltage of the cells will decrease individually again, and imbalance will return. Whole procedure took me 2 hours, so i will repeat it if needed.
I'm glad it helped you. Your approach is fine. Charging with 5V should not do any harm as long as the actual battery voltage is monitored and does not exceed 4.1V (absolute max. 4.2V). There is a good chance that the problem will return in the future as the battery management is poorly designed and does not take into account the individual condition of the cells. As a result the cells tend to drift apart. The only option is to correct them from time to time. It is recommended to charge the battery to around 60 % before storing it for a longer period of time in order to avoid an undervoltage shutdown.
Good day and thanks for the instructions so far. My question is where to load the cells? Should I connect my charger to the steel clamps on the top, like the original charger does, or do I need to connect to the cells at the tin spots at the corners which are marked by the red lines on your picture? The steel clamps are marked with +, E, TH and -
Thanks for the question. It is important that you connect to the terminals of the individual cell and therefore use the tin spots I marked in my picture. If you were to use the terminals that the charger uses only the whole pack (all 3 cells together) could be charged. To solve the problem each cell must be charged individually. Best regards. Joel
Hello I have problem with charging, when I connect the battery it doesn't charge, the red light on the charger comes on, but after 10 seconds the green light comes on that the battery is charged but it is not, please help.
Hi. The charger cannot charge the cells individually but the cells are still monitored individually. This means that if one cell has already reached its final voltage of about 4.1 volts the charging process is considered completed even though the others have little or no charge. This results in a total voltage that is too low to start the mower. In this case this indicates also an imbalance and the method in this guide should also help.
Good morning, my set no longer had power, so I replaced the cells with new Sony VTC4, please charge the charger again, after a while the green LED lights up again, indicating that the battery is charged, however, there is no voltage on the power connectors and the mower does not start, please, where is the problem, the cells have currently the voltage is 4.150V each, I charged them with an external charger. Thank you
It is difficult to say what the problem exactly is. The charger is completing the charging of the pack (green) as soon as an individual cell is fully charged, regardless of the status of the other cells. So this seems expected in your case.
Please measure the total voltage of the whole battery pack (+ to -). This should correspond to the sum of the individual cell - approx. 12.4 volts. If this is not the case, a cell may not be connected correctly or may have been installed with the wrong polarity. The mower will only start if the total voltage is high enough (>= 10.8V).
As a last option it could also be that one cell is bad or old which results in a high internal resistance. This would result in massiv voltage drop under load and the voltage might not be sufficient to start the mower. Let me know if you need more infos on how to measure this.
I really hope this will help you to solve the issue.
Regards. Joel
