Anyone else had grief with JK BMS dropping Bluetooth after a firmware update?

Updated my JK-B2A8S20P to firmware 11.25 last week and ever since the Bluetooth has been practically useless. It connects for maybe 30 seconds in the App, then just drops and won't reconnect without a full power cycle of the BMS. Before the update it was rock solid — I could leave the app open all day no bother.

Running an 8S 24V 280Ah LiFePO4 pack built from EVE cells, wired up in the van alongside a Victron SmartSolar 100/30 and a Multiplus-C 12/2000 (yes I know, 12V inverter on a 24V system — long story, different thread). The BMS itself seems to be doing its job fine, balancing looks normal and charge/discharge is behaving, it's purely the Bluetooth comms that's gone to pot.

I've tried deleting and reinstalling the JK BMS App, tried it on two different Android phones (one running Android 12, one on 13), and I've had a poke around on the JK Wiki but can't find anything useful. Has anyone managed to roll back to an older firmware, or found a fix? I've seen a few mentions of this on some Facebook groups but nothing concrete. Bit reluctant to contact the AliExpress seller as it always takes forever to get a useful response.

@Chunk75 yeah, seen this exact thing on mine after a similar update. Worth trying a full power cycle of the BMS itself (not just the app) — disconnect load and charge sides completely, wait 30 seconds, reconnect. Fixed it temporarily for me.

Long term though, I rolled back to 11.18 which has been rock solid. JK's firmware release notes are basically nonexistent so you're flying blind with updates tbh.

Also check you haven't got something else competing on 2.4GHz nearby — my Victron Cerbo was causing interference until I moved the BMS slightly.

If rollback isn't an option, some people run a cheap Bluetooth-to-RS485 adapter and just ditch the BT entirely. Bit of faff but more reliable day-to-day.

@Chunk75 had this on my static van build last summer — different firmware version but same disconnect behaviour. What fixed it for me was going into the app settings and disabling the auto-sleep function on the BMS. It's buried in the advanced parameters somewhere. Basically it was dropping BT as part of a sleep cycle and then not waking properly.

Also worth checking if your phone's Bluetooth is doing its own power saving — Android especially will kill BT connections aggressively in background. Had to whitelist the JK app specifically.

If neither works, the JK Facebook group has a pinned thread with a rollback procedure to get back to the previous firmware. Bit of a faff but sometimes that's the easiest route.

Hey @Chunk75, frustrating one this. I had something similar on my B2A8S20P and what actually sorted it for me was going into the app settings and disabling the "Bluetooth sleep" or low-power mode option — it's buried in the device settings rather than the app itself. The newer firmwares seem to be more aggressive about dropping the BT radio to save power. Also worth checking you're running the latest version of the JK BMS app rather than an older cached install, as there was a companion app update that addressed some reconnection handshake issues. If neither of those help, @IslandCruiser's experience might point toward it being firmware-specific — do you know which version you were on before 11.25? Might be worth considering a rollback if JK have the previous firmware available on their site.

@Chunk75 worth checking whether your phone's Bluetooth cache might be making things worse — go into your phone's app settings, clear the cache and stored data for the JK BMS app, then forget the device in your phone's Bluetooth settings entirely before attempting a fresh pair. I've found Android in particular holds onto old connection data that seems to confuse the BMS after a firmware change. Also, how far away are you when it drops? The 11.x firmware versions seem to have reduced the effective range noticeably on a few units I've heard about. Try staying within about a metre when reconnecting initially. Curious what @KentOffGrid's fix was too — their reply got cut off!

@Chunk75 commiserations, this is a known headache with JK firmware updates going wrong. One thing worth trying that nobody's mentioned yet — check whether the Bluetooth module itself has gone into a low-power state it's struggling to wake from. In the JK app, go into the device settings and look for the Bluetooth sleep timer option; some firmware versions reset this to a very aggressive timeout. Setting it to disabled or maximum has sorted it for a few people I've seen report this on other forums. Also worth making sure your phone's battery optimisation settings aren't killing the app in the background, as Android in particular can be brutal with that. If neither helps, @KentOffGrid's suggestion (whatever it was — curious now!) and @BirchLover's power cycle are solid starting points before considering a rollback.

Hey @Chunk75, gutting timing on that update! Just to add to what the others are saying — have you tried toggling the BMS Bluetooth off and back on via the physical button on the unit itself rather than through the app? On mine that seemed to reset the connection stack properly rather than just dropping and retrying from the phone side. Also worth making sure you're within about 3 metres when initially pairing after a drop — I found the signal strength on 11.x firmware seems noticeably weaker than before during the handshake phase. If none of that helps, JK do have older firmware versions available if you contact their support directly and ask nicely — downgrading to 11.22 sorted a few people out on another forum I use. Good luck with it!

My JK on the shepherd's hut did exactly this — turns out the fix was embarrassingly simple: power-cycle the BMS completely (disconnect both load and charge sides so it goes fully dead), wait 30 seconds, then reconnect. Something about the Bluetooth stack needing a proper cold boot rather than a soft reset. @Chunk75 worth trying before you go down the firmware rollback rabbit hole, which is its own special kind of misery.