4S - Using 4 Batteries in Series

4S BMS Protect Four (Groups of) Batteries From Mishap. Combined With Balancing They Are A Perfect Fit For Your Batteries.

A 4S BMS is needed to protect four batteries (or groups of batteries connected in parallel) that are connected in series.

BMS often ship in locked state: no output voltage is available at the output pins.
Locked state is 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 you use wires with sufficient diameter for the anticipated high currents.
Also make sure you only use batteries of same type and same state of charge. 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.

List of 4S BMS

Here is a list of actual 4S BMS breakout boards, separated by maximum current:


Please do leave comments below. I am using utteran.ce, an open-source and ad-free light-weight commenting system.

Here is how your comments are stored

Whenever you leave a comment, a new github issue is created on your behalf.

  • All comments become trackable issues in the Github Issues section, and I (and you) can follow up on them.

  • There is no third-party provider, no disrupting ads, and everything remains transparent inside github.

Github Users Yes, Spammers No

To keep spammers out and comments attributable, all you do is log in using your (free) github account and grant utteranc.es the permission to submit issues on your behalf.

If you don’t have a github account yet, go get yourself one - it’s free and simple.

If for any reason you do not feel comfortable with letting the commenting system submit issues for you, then visit Github Issues directly, i.e. by clicking the red button Submit Issue at the bottom of each page, and submit your issue manually. You control everything.


For chit-chat and quick questions, feel free to visit and participate in Discussions. They work much like classic forums or bulletin boards. Just keep in mind: your valued input isn’t equally well trackable there.

  Show on Github    Submit Issue

(content created Feb 27, 2024)