Problem

The series-connected battery bank appears to have significantly less available energy than expected, leading to potential early cutoff during charging or discharging.


Possible Cause

This issue may arise from various factors, such as differences in storage conditions, batteries from different batches, or varying usage patterns. When batteries with different states of charge are connected in series, it can result in imbalances within the battery bank. One battery may be the first to reach full discharge, triggering a disconnect during discharging, while another may be the first to reach full charge, leading to a charger disconnecting. It's important to note that the Battery Management System (BMS) is designed to handle small cell-to-cell variations (up to 2.5% imbalance) but not larger imbalances between differently used batteries. Even a slight variation in open circuit voltage can indicate a significant difference in the state of charge. The best way to identify an imbalanced battery is when it is either fully charged or fully discharged.


Solution

To address this issue, follow these steps:

  1. Disconnect the batteries and recharge them individually using a 2-stage charge, tapering to ≤0.05C for each battery.
  2. To expedite the process, you can connect batteries in parallel, but limit this to a maximum of two (2) cells.

Always adhere to recommended specifications when charging batteries.