Monday, October 13, 2025

What Really Occurs When Lithium Batteries Are Paralleled? Uncovering Voltage and BMS Dynamics

Imagine two water buckets connected by a pipe. This is like connecting lithium batteries in parallel. The water level represents voltage, and the flow represents electric current. Let’s break down what happens in simple terms:

Scenario 1: Same Water Level (Matched Voltage)​​

When both "buckets" (batteries) have identical water levels:

  • Charging (adding water):​​Current splits evenly between batteries
  • Discharging (pouring out):​​Both batteries contribute power equallyThis is the ideal and safest setup!

​Scenario 2: Uneven Water Levels (Voltage Mismatch)​​

When one bucket has higher water level:

  • Small difference (<0.5V):​​Water flows from high to low bucket slowlyA ​​smart faucet (BMS with parallel protection)​​ controls the flowLevels eventually balance
  • ​​Large difference (>1V):​​Water rushes violently to the low bucketBasic protection shuts down the connection

lithium battery connectionparallel battery safety

Scenario 3: Different Bucket Sizes (Capacity Mismatch)​​

Example: Small battery (24V/10Ah) + Large battery (24V/100Ah)

  • ​​Same water level (voltage) required!​​
  • Discharging at 10A:​​Small battery supplies ~0.9ALarge battery supplies ~9.1A
  • ​​Key insight:​​ Both water levels drop at same speed!

NEVER Mix These!​​

​​Different pump types (discharge rates):​​

  • Strong pump (high-rate battery) pushes too hard
  • Weak pump (low-rate) gets damaged quickly
  • Can cause overheating or fire!

3 Golden Safety Rules​​

  1. ​​Match water levels:​​ Check voltage with multimeter (difference ≤0.1V)
  2. Use smart faucet:​​ Choose BMS with ​​parallel current control​​
  3. Same bucket type:​​
    • Identical capacity
    • Same chemistry (e.g., both LiFePO4)
    • Matching pump power (discharge rate)

Pro tip: Parallel batteries should behave like twins!

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Company Name: DALY BMS
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Country: China
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