Anyone else had issues with a Renogy 40A MPPT playing up in cold weather?

Had this exact problem with mine last winter on the boat. Temps dropped to around -3°C overnight and the controller was throwing low voltage faults first thing in the morning even though the batteries were fine. Turned out it was the controller itself struggling rather than anything actually wrong with the system.

A few things worth checking:

• Ambient temperature compensation — is yours set correctly for your battery chemistry? Mine was misconfigured out of the box
• The display ribbon cable — on colder mornings mine would show garbage readings until it warmed up a bit, which I eventually traced to a dodgy internal connection that got worse when the casing contracted in the cold
• Firmware — Renogy pushed an update a while back that apparently addressed some low-temp behaviour, worth connecting to the BT module app if you have it

Honestly I ended up replacing mine with a Victron SmartSolar 100/30 and haven't had a single issue since. The Renogy wasn't terrible value but the Victron's temperature handling is just in another league, especially with proper Bluetooth monitoring through VictronConnect.

That said, plenty of people run Renogy gear through UK winters without drama. Could be a dud unit rather than a design-wide issue.

What batteries are you running — lithium or lead? That changes the diagnosis quite a bit. Also, where is the controller physically mounted? If it's in an uninsulated locker it'll be seeing the same temps as outside.

Anyone else got experience with Renogy cold weather behaviour? Curious whether this is more widespread than I thought.

@BrianBrown — classic cold-soak behaviour. The MPPT's internal temperature compensation is likely miscalibrated or the battery temp sensor isn't fitted (or is reading ambient air rather than actual cell temp).

At -3°C a lead-acid bank's resting voltage drops noticeably, so the controller sees "low voltage" even though the bank is reasonably healthy — it's just cold physics.

A few things worth checking:

• Battery temp sensor — is it actually clamped to a cell terminal, not just dangling nearby?
• Absorption setpoints — these need lifting in winter; Renogy's defaults are quite conservative
• Battery type setting — if it's set to sealed/AGM when you've got flooded, the voltage thresholds will be off

I had similar grief with my Renogy 40A before switching to a Victron SmartSolar — Victron's app lets you fine-tune temperature compensation coefficients properly, which made a huge difference on cold mornings.

@BrianBrown worth checking whether your battery temp sensor (if you've got one fitted) is actually reading correctly or has come loose from the battery surface. I had almost identical faults on my garden office setup last January — turned out the sensor had lifted off the terminal and was reading ambient air temp instead of the battery, so the controller was massively over-compensating the voltage threshold downward in the cold.

Also, lithium or lead-acid? If it's LiFePO4 with a BMS that has low-temp charge protection, the BMS itself may be blocking charge acceptance at -3°C regardless of what the MPPT thinks it's doing — at which point the controller sees a "dead" battery and panics. Fogstar Drift cells have this protection built in. Worth ruling that out before blaming the Renogy itself.

Something similar happened to me last winter parked up in the Cairngorms — woke up to the Renogy showing all sorts of nonsense despite the batteries being absolutely fine when I checked them with a multimeter.

What I eventually traced it back to was the controller itself getting so cold overnight that its own internal reference voltage was drifting. The unit was mounted in an external locker with no insulation around it whatsoever.

Moved it inside the motorhome near the habitation area and the problem vanished completely. Dead simple fix that cost nothing.

Worth noting that Victron controllers handle cold-soak noticeably better in my experience — they're built with wider operating tolerances. If the Renogy keeps misbehaving, @BrianBrown, that might be your longer-term answer, though obviously it's a bigger outlay.

@MarineVicky the Cairngorms in January — brave soul!

I had almost identical grief with mine in my garden office setup last February when we had that brutal cold snap. What finally cracked it for me was realising the controller itself was mounted on an exterior wall, so it was cold-soaking right alongside the batteries overnight. Moved it inside the insulated wall cavity and the phantom faults stopped almost immediately.

The Renogy's temperature compensation algorithm genuinely struggles when the controller is cold rather than just the batteries — it's reading wonky internal temps and adjusting voltage thresholds based on that rather than actual battery conditions.

@BrianBrown on a boat you've probably got less flexibility, but even wrapping the controller in a bit of closed-cell foam insulation made a noticeable difference for a mate of mine on a narrowboat. Worth trying before you start chasing sensor gremlins.

@BrianBrown one thing worth investigating that nobody's mentioned yet — the Renogy 40A has a known quirk where the low-temp lithium charging cutoff can trigger prematurely if the unit itself is mounted somewhere exposed rather than the battery being the cold component.

The controller's internal temp sensor influences its behaviour, and if it's reading -3°C ambient, it may refuse to push charge regardless of what your battery temp sensor says — essentially the two readings conflict and it defaults to conservative/fault mode.

If you're running LiFePO4, check whether your BMS has its own low-temp cutoff configured independently, because you can end up with two systems both trying to protect the battery and neither communicating with the other.

On my shepherd's hut build I moved the MPPT inside the insulated cabinet alongside the batteries — ambient temps stayed consistent and the spurious faults disappeared entirely.