4S 25A Battery Management Systems (BMS)

BMS For Four Battery Strings And 25A Max Current

BMS often ship in locked state: no output voltage is available at the output pins. Locked state is also entered whenever over-current protection was triggered. To unlock the BMS, connect it to a charger. If you did not add a dedicated charger board, apply the appropriate charging voltage to its output terminal.

When connecting batteries to your BMS, make sure to use wires with sufficient diameter for the anticipated high currents.

When designing battery packs, use batteries of same type and same state of charge only. It is recommended you fully charge all batteries before connecting. All batteries must have the same voltage (voltage difference less than 0.05V). Do not mix batteries from different vendors, types, capacity, or age.


LiIon LiPo

For currents up to 25A, this rounded multi-purpose board is available:

Connect the batteries like this:

  • First battery string to B- (-) and B (+)
  • Second battery string to B (-) and B1 (+)
  • Third battery string to B1 (-) and B2 (+)
  • Forth battery string to B2 (-) and B+ (+)

The output voltage is available at P+ and P-. These two pads are accessible from both sides.

The terminal A is not used. It is reserved for the 5S version of this board.


Protection Threshold
Over-Charge >4.25V
Over-Discharge 2.8V
Over-Current 60A
Short Circuit yes,resettable
Continuous Current 25A
Size 50x22x4mm


When charging batteries through this BMS, the charging voltage needs to be 16.8-17.0V. The BMS limits the charging current to 25A.

Changing BMS Type

This is a multipurpose board and can be used for 3S, 4S, and 5S. The number of supported strings can be configured on the board at four locations:

Location 3S 4S 5S
1 unconnected 0R unconnected
2 0R unconnected unconnected
3 0R 0R unconnected
4 0R unconnected unconnected

0R refers to a 0-Ohm resistor (a solder bridge). If you’d like to change the configuration of your BMS, you can remove 0R resistors (to switch to unconnected), or bridge the pads with solder (to switch to 0R). No need to try and move around and re-solder the tiny 0R resistors.

For 3S BMS, connect the batteries like this:

  • First battery string to B- (-) and B1 (+)
  • Third battery string to B1 (-) and B2 (+)
  • Forth battery string to B2 (-) and B+ (+)

For 5S BMS connect the batteries like this:

Connect the batteries like this:

  • First battery string to B- (-) and A (+)
  • Second battery string to A (-) and B (+)
  • Third battery string to B (-) and B1 (+)
  • Forth battery string to B1 (-) and B2 (+)
  • Fifth battery string to B2 (-) and B+ (+)


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(content created Mar 16, 2024)