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Sunsynk F58: Battery BMS Communication Fault

Updated June 2026 · Reviewed for technical accuracy · ~3 min read

F58 means your Sunsynk has lost the conversation with the battery's BMS (Battery Management System). The two devices normally swap data constantly so the inverter knows exactly how to charge and discharge a lithium battery. When that link drops, you get F58. The good news: the usual culprit is a simple communication cable, not the battery itself.

The usual causes, most common first

  • A loose comms cable. The thin RJ45 (network-style) cable between battery and inverter has worked loose at one end. By far the most frequent cause.
  • The wrong battery protocol selected in the inverter, so the two "speak different languages".
  • Wrong port or DIP-switch address, common when batteries are stacked.
  • The battery is off or asleep, so there is nothing to talk to.

How to fix it safely

Low-voltage only You are touching the thin comms cable and the menu, never the battery's main power terminals.
  1. Check the battery is awake. Make sure it is switched on and not in sleep or protection. Wake it if needed.
  2. Reseat the comms cable. Unplug the RJ45 cable at both ends and click it firmly back until it latches. Look for a snapped clip.
  3. Confirm the correct port. The cable must be in the CAN (or RS485) port your battery uses. Sunsynk and the battery maker both document which.
  4. Select the right battery protocol. In the Sunsynk's battery settings, pick the exact battery brand or protocol you own. The wrong choice causes a constant F58.
  5. Check stacked-battery addresses. With more than one battery, verify the DIP-switch addresses follow the maker's order.
  6. Restart. Power-cycle the inverter so it re-handshakes with the BMS.

Quick decision flowchart

F58 appears
↓ reseat cable, confirm port + protocol
✅ Comms restored (battery data shows again) → solved.
❌ Still no comms with a known-good cable + correct settings → battery BMS or port fault.
↓
If it persists, contact your installer or battery maker. The BMS or comms port may be at fault.
About the "disable BMS error stop" option Sunsynk lets you switch off the BMS error stop so it stops alarming. Only do this if your system is deliberately running in voltage mode without BMS comms. On a normal lithium setup you want the BMS talking to the inverter, so don't just silence a real fault, because the BMS is what protects the battery.

Related Sunsynk codes

F56, DC bus voltage low F24, DC insulation failure F64, Heatsink high temp

FAQ

My battery still charges, so why does F58 matter?

Without BMS comms the inverter may fall back to voltage-based charging, which is cruder and can stress a lithium battery over time. Restore the link so the BMS can manage the limits properly.

I changed nothing and F58 just appeared.

Vibration, temperature swings or a firmware update can unseat a marginal cable or reset a setting. Start by reseating the comms cable, which fixes most "it just showed up" cases.

Which cable is the comms cable?

It's the thin network-style (RJ45) cable between the battery and the inverter's CAN/RS485 port, not the thick power cables on the battery terminals. Only handle the thin one.

Sources

  • Sunsynk Hybrid Inverter User Manual (F58 = BMS communication fault; check cables or the BMS error-stop setting).
  • Sunsynk fault-code references; common cause documented as a loose RJ45 comms connection.
⚠️ Safety disclaimer. Battery systems store large amounts of energy and can carry lethal voltage. This guide covers the low-voltage comms cable and settings only. Never touch battery power terminals or open equipment unless qualified. When in doubt, call a licensed installer or your battery manufacturer.