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How to monitor your JK BMS battery in Chrome over Bluetooth (BatRay, nothing to install)

11 Sep 2026

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TL;DR: open clearevo.com/batray in Chrome, press Connect, pick your JK BMS. Voltage, state of charge, current, power, every cell, temperatures, capacity and cycles, live. Nothing to install.

Connect

1. Bluetooth on. Android: Chrome. PC: Chrome or Edge. (Not iPhone, not Firefox.)
2. Open https://www.clearevo.com/batray/, press Connect.
3. Pick your BMS in the list. It shows under whatever name was set in the JK app (mine is n11, my name for the NMC 11 kWh bank).
4. Readings appear in a few seconds and refresh every 3 s. Close the JK app first: a JK BMS takes one Bluetooth connection at a time.

No BMS nearby? Press Demo: a simulated pack, labelled DEMO.

Leave an old phone next to the battery

Any old Android phone, tablet or notebook with Chrome becomes a permanent monitor. Plug it in, connect once, leave the tab in front. The screen stays awake by itself, and if Bluetooth drops it reconnects every 10 s until you press Cancel. Leave the phone asleep for an hour and Android freezes the tab: BatRay throws away whatever the Bluetooth stack queued up meanwhile and reconnects for fresh readings, so what you see on your return is never an old number dressed up as live. If the screen still sleeps: Android Developer options → Stay awake; on a notebook, turn off sleep.

Watch from anywhere

Press Share live. A link is copied; open it in Chrome on any phone or PC and you see the same screen, live. Both ends show how many people are watching and how much of the free server is in use. With Chrome notifications on, the reader (the phone next to the battery) is told when a viewer joins or leaves, a viewer is told when the reader goes offline or comes back, and either side is told when its own internet drops or the server stops answering, so you always know which one it is. Anyone with the link can watch, so treat it like a password; stop sharing makes it dead. Readings are encrypted on your phone with a key that exists only inside the link, so nobody in between can read them, not even clearevo.com.

More than one BMS

Press + Add BMS. Every pack is read at the same time; tap a chip to switch. A shared link carries all of them.

Alerts

Open Alerts under the meters and tick Chrome notifications (Chrome asks once for permission; send a test shows one). Five rules are already on: battery below 40 %, below 25 %, no charging in daylight, cells drifting apart, and no data from the BMS. Change or switch off any of them. Notifications pop up on this device while the tab is open; on Android keep the tab in front.

What you see

• Meters: pack voltage, state of charge, current and power. Amber discharging, green charging.
• Check line: ✔ means the pack voltage agrees with the sum of the cells, so the numbers are decoded right. ⚠ layout uncertain means do not trust them; press Copy log and send it to me.
• Cells: one bar each, lowest amber, highest blue. The bars exaggerate the spread on purpose; read the mV figure.
• More and BMS settings: everything else the BMS reports, and its protection limits. Read-only: BatRay never writes to the BMS.

Limits

• Chrome or Edge only, Android or desktop. No iPhone.
• Read-only. No history charts, no switching anything.
• Tested on my own unit and on captured frames from four JK firmware generations; a new firmware may show ⚠. Send the log.
• Notifications need the tab open and, on Android, in front.

Privacy

Battery data stays on your device unless you turn on Share live, and then it goes to your viewers encrypted, unreadable to anyone in between, clearevo.com included. Alerts are judged and shown on the device; nothing is sent. Google Analytics counts visits only - verify it yourself.

Licence

© 2026 Kasidit Yusuf. Free software under the GNU GPL v2, like every ClearEvo tool. Provided as is, with no warranty and no support. Not a safety device: BatRay cannot be relied on to prevent damage or danger.

This tool is free software and open source: ykasidit/clearevo_online_tools (public/batray) - issues and pull requests welcome, especially captured frames from JK firmware I do not own.

Full disclosure: this post - and any code or tool it describes - was co-authored with Claude (Anthropic’s AI, via Claude Code). I directed, guided and reviewed. I don’t want to pretend otherwise.

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