Eco-Worth 5kw Solar off-grid inverter and two Power Mega 314 AH Lithium Batteries getting a fault 5

Had a similar headache with my shepherd's hut setup last year — not the same kit, but fault codes on cheaper inverters often come down to a handful of culprits worth ruling out.

Fault 5 on most budget inverters typically points to an over-voltage or battery communication issue. A few things I'd check:

• Are your 314Ah batteries wired in series or parallel? If parallel, uneven cell balancing between the two packs can confuse the inverter's BMS handshake
• What's the resting voltage showing on each battery individually? Worth disconnecting them and checking separately
• Cable gauge and connection quality — undersized DC cables cause voltage drop under load, which can trigger faults even when everything looks fine on paper

The Power Mega batteries — are they proper LiFePO4 with a built-in BMS, or are you relying on the inverter to manage them? Some of these lesser-known brands have BMS boards that don't communicate cleanly with inverters outside their own ecosystem.

If you were running Victron or similar, there'd be proper CAN bus integration and you'd see exactly what's happening. With budget gear talking to budget gear, sometimes it's just trial and error.

What load were you running when the fault appeared? Startup surge from something like a fridge compressor or kettle can trip it if the low-voltage cutoff is set too conservatively.

Would be useful to know your full setup — panel wattage, charge controller type, and whether the fault clears on restart or stays latched. Others on here have probably seen this exact combo.

@TerryScott72 makes a fair point about the usual suspects, but with that specific combo I'd look hard at the BMS communication first. The Power Mega batteries — are they set to lithium mode on the Eco-Worth, or is it still defaulting to AGM/gel? That'll throw a Fault 5 on a lot of these budget inverters because the charge profile is completely wrong and the BMS trips out protectively.

Also check your battery cable gauge and connections. 314Ah cells can pull serious current on inverter startup — undersized cables cause voltage sag and the inverter panics.

Not familiar with Eco-Worth specifically, but I've seen near-identical fault behaviour on a cheap unit I had in my garden office before I switched to Victron. The inverter was simply lying about what the fault actually was.

What's your cable run length between batteries and inverter?

@VoltWill is right to flag the BMS comms side, but worth adding: those Power Mega batteries often use a fairly generic JK-BMS underneath, and Fault 5 on budget Chinese inverters almost universally maps to low battery voltage cutoff being triggered during a high-load spike — even when resting voltage looks healthy.

Check your cable cross-section and lug crimps between batteries and inverter. I've seen 16mm² where 35mm² was needed, causing enough voltage sag under load to trip the fault. Voltage at the battery terminals under load is what matters, not idle readings.

Also — are your two 314Ah batteries wired in parallel with equal-length cables? Unbalanced parallel banks cause one battery to take the brunt and its BMS throws the towel immediately.

What's the inverter showing for battery voltage at the moment of fault?

Good shout from @TracyAllen on the generic BMS side — worth checking if your inverter even supports that battery protocol properly. Eco-Worth isn't exactly top tier for compatibility.

One thing nobody's mentioned: cable sizing and connection torque. Fault 5 on a lot of these budget inverters can trigger from voltage sag under load rather than a true fault. Had something similar on a cheap inverter before I switched to Victron — turned out my negative busbar connection was barely finger-tight.

Try:

• Check all terminals are properly torqued
• Measure actual voltage at the battery terminals under load
• Compare to voltage at the inverter input

If there's more than 0.3–0.5V drop across your cables, that's your culprit before you even touch the BMS settings.

@BatterySam raises a valid point on protocol support — worth actually pulling up the Eco-Worth manual and checking whether it expects a proprietary UART comms signal or just operates on voltage/current sensing alone.

On the narrowboat I ran a similar budget inverter for a while before switching to Victron. The fault codes on those cheaper units can be deceptive — "Fault 5" might not be comms at all depending on firmware version.

A few things worth trying before assuming it's BMS comms:

• Check DC cable sizing — undersized cables cause voltage sag under load which can trigger protection faults
• Confirm battery low-voltage cutoff settings match what the BMS is actually reporting
• Are both 314Ah batteries wired in parallel? If so, are they identical firmware versions?

What's the actual load when the fault triggers?