Anyone else had grief with JK BMS dropping Bluetooth mid-charge on a 280Ah LiFePO4 bank?

Picked up a JK BMS (the 200A active balancer version) back in January to run with four 280Ah EVE cells I got from Docan. Been really happy with the setup overall — cells are rock solid and the balancing seems to do its job. But I've got this really annoying issue where the Bluetooth drops out almost every time the bank hits around 90% SOC during a solar charge. Phone's sat right next to the unit and it just disappears from the app. Reconnects fine once charging slows down or stops.

It's not a huge deal in practice but I'm trying to log charge cycles properly and it keeps breaking the data. I'm running the JK BMS app on Android 13 (Samsung S21) and I've tried two different phones with the same result. Firmware on the BMS is showing 11.25 — not sure if that's the latest or not, I can't find a clear changelog anywhere.

I've read somewhere it might be a power draw issue causing the Bluetooth module to brown out slightly when the balancer kicks in hard near top of charge, but that's just forum speculation really. Has anyone actually resolved this or found a workaround? Wondering if a firmware update would sort it or if it's just a known quirk I need to live with.

Jonno88 | 47 posts

@Ian1968 yeah had exactly this with mine last summer. Turned out the Bluetooth drops were linked to the BMS working harder during balancing — the chip apparently gets a bit thermally stressed and the BT radio is first thing to back off.

Worth checking if it coincides with your cells being slightly out of balance (say 3.38V vs 3.42V range) as that's when the active balancer kicks in properly and current draw on the board spikes.

My fix was dead simple — made sure there was a bit of airflow around the BMS rather than it being stuffed in a box. Sorted it completely.

Also make sure you're on the latest firmware via the JK app, there were some stability updates pushed out late last year that helped a few people on here with similar issues.

Chalky12 | 134 posts

@Ian1968 worth checking the firmware version on that JK — there was a batch shipped around Q4 last year with dodgy BT stack behaviour specifically during active balancing cycles when cell delta goes above ~20mV. The balancer kicking in seems to briefly spike the BMS processor load and BT just gives up.

Download the JK BMS app on Android (iOS version is flakier in my experience) and check if a firmware update is available via the app itself. Fixed mine stone dead.

Running a 4x280Ah EVE bank myself with a Victron SmartShunt alongside the JK — I log everything through VRM so even if BT drops on the JK I've still got visibility. Might be worth doing something similar as a belt-and-braces approach while you sort the underlying issue.

BMS_Geek | 203 posts

Running the same JK 200A active balancer on my boat bank (EVE 280Ah cells, also from Docan as it happens). Had the Bluetooth dropout issue twice — both times traced it back to the phone being the problem, not the BMS. Android background app restrictions were killing the connection.

That said, worth checking your cell voltage spread during bulk charge. If any cell is hitting the high voltage cutoff while the others lag behind, the BMS can do odd things with connectivity — almost like it's throwing a wobbly while trying to protect simultaneously.

Download the JK app on a different device and test. Also make sure you're within a couple of metres when connecting — the Bluetooth antenna on these units is genuinely weak compared to something like a Victron SmartShunt.

IvyWalker | 23 posts

@Ian1968 interesting one — I've got a similar setup in my static caravan, 280Ah EVE cells with a JK BMS (the 100A version though). Mine drops Bluetooth when the Victron MPPT kicks in hard on a sunny morning. Wondered if it's interference from the charge controller rather than a BMS fault itself?

Have you tried physically separating the BMS from any cabling runs? I moved mine about 30cm away from the main DC bus and it seemed to reduce the dropouts noticeably.

Also curious whether you're monitoring via the JK app directly or pulling data through something else — I've been meaning to integrate mine with a Cerbo GX but not got round to it yet. Does the BMS itself continue functioning normally when Bluetooth drops, or are you seeing actual charge interruptions too?

MuddyRanger | 67 posts

@Ian1968 Had something similar on my shepherd's hut build — turned out the Bluetooth dropout was heat-related rather than firmware. The JK was mounted in a fairly enclosed battery box and once charge current ramped up, the BMS housing was getting warm enough to cause issues.

Moved it to a spot with better airflow and haven't had a dropout since. Worth ruling out before you go down the firmware rabbit hole.

Also — are you monitoring through the JK app directly or via a Victron MPPT? I had some weird interference when both were polling the BMS simultaneously over Bluetooth. Disabling the Victron's Bluetooth temporarily helped me narrow down what was actually causing the drops.

WingAndPrayer88 | 412 posts

@Ian1968 Worth checking your phone's Bluetooth settings — specifically whether it's treating the JK app as a background process and killing it to save battery. Android is notorious for this. On Samsung particularly, go into Battery > App Power Management and whitelist the JK BMS app, then disable "Adaptive Battery" for it. Made a massive difference on mine during bulk charge when the phone screen was off.

Also, if you haven't already, try the newer JK firmware — I flashed mine about three months back and the connection stability improved noticeably. You'll need a USB-to-TTL adapter to do it properly rather than OTA. Bit faffy but worth the hour it takes.

What firmware version are you currently on? Should show it in the app's device info screen.

LochSpirit | 891 posts

@Ian1968 One thing nobody's mentioned yet — the JK BMS Bluetooth module shares the same ground reference as the balancer circuitry. During active balancing on a near-full bank, you can get enough noise on that ground line to cause the BT stack to reset. I replicated this exact fault on my garden office build (4× EVE 280Ah, same JK 200A unit).

Fix that worked for me: shielded twisted-pair on the comms cable, grounded at one end only. Dropped out roughly every 8–12 minutes before; zero dropouts since. Also worth upgrading to the latest JK firmware — there was a specific BT stability patch released late 2023.

MaxFrost | 34 posts

@Ian1968 Seeing this on my boat setup too — JK 200A with EVE 280Ah cells, same as yours. Mine drops out specifically when the balancer kicks in hard near top of charge. I've started using a USB-to-RS485 adaptor and the PC software instead when I actually need to monitor a full charge cycle. Not ideal but it's rock solid compared to Bluetooth. Also worth asking — are you running this as emergency backup only, or continuous cycling? Mine seems worse when it's been sitting unused for a while before a charge.