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Problem diagnosis · Off-Grid · All brands

Off-grid solar not charging

Your panels are producing power but the battery isn't charging — or the MPPT controller is showing zero amps despite bright sunshine. This affects all off-grid brands: Victron SmartSolar, EPsolar, Tracer, Renogy, Outback, SMA, and others.
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Excellent knowledge and service. Ron responded to my initial query really quickly (same day), and confirmed that he could add extra panels and battery to my existing GivEnergy setup - something I’d been told by other installers wouldn’t be possible. Two weeks later (!), scaffolding was up and Ron and his team were on site to fit the extra 5 panels and two more GivEnergy batteries. I now have a truly optimised system, which has made the most of the south facing roof space I have, without having to start again with new kit. I’m now generating enough on the solar to fill my batteries, and avoid using the grid. I’ve also exported far more than before. Brilliant experience, well recommended.

Mark Emery · Jul 2026 Google

Ron is one of those rare finds - an engineer's engineer. He insightfully and accurately diagnosed the problems with our GivEnergy system, very quickly, which helped get us back on track. We will be using him again!

Geoff Palmer · Sep 2026 Google

Absolutely wonderful. Would recommend without hesitation. I had an issue I was thinking would never be fixed and they fixed it. Help, advice and support every step of the way. I can't recommend highly enough. Thank you so much ⭐

jill brocklehurst · Jul 2026 Google

I had a red status light on my GivEnergy battery pack and Ron at Solar Tech Support was a great help resolving the problem. He was able to do a remote diagnosis of the invertor BMS firmware and hardware and gave very quick practical and professional support. Thanks Rob

Rob Heminsley · Jul 2026 Google

Ron was brilliant. He really tried to help. He spent hours trying to fix our GivEnergy AIO and ultimately it became apparent that it needed parts to fix the BMS management system. As there appears to be no replacement parts available on the market, he gave excellent advice on what options are now available to move forward. He is incredibly helpful and knowledgeable.

Mark Mayson · Jun 2026 Google

My installer put me through Hell with so botched install that you can not imagine Than Ron came , He did not managed to do miracles (because my system components were impossible to work together) and he Gave me a detailed report of what is wrong , why is wrong , why can not be fixed etc. with all the details which I can use in a claim. Without His his help knowledge and attitude I would've been lost

Boris · Oct 2026 Trustpilot

Written by · Independent Solar Engineer Last updated

Safety Warning

Do not open your inverter or interfere with DC cabling. Solar panels produce live DC voltage whenever exposed to light. Always use your DC isolator switch and contact a qualified solar engineer for hands-on fault diagnosis.

Off-grid charging is different from grid-tied charging. Grid-tied hybrid inverters report charging faults through their monitoring portals and usually diagnose themselves. Off-grid MPPT controllers often have minimal displays and communicate faults through LED codes or simple numeric error codes. The diagnosis sequence below covers both simple and advanced controllers.

Diagnostics

5-step off-grid charging diagnosis

Work through these in order. Each step rules out a cause and narrows down what to check next. You don't need specialist equipment — a multimeter helps for step 3 but is not essential.

1

Check the MPPT controller display for fault codes and PV input readings

The controller tells you what it can see. Check for active fault codes and note the PV voltage reading:

What the PV voltage reading tells you
PV voltage = 0V: No power reaching the controller — blown fuse, open circuit, or damaged panel/cable.
PV voltage = battery voltage: MPPT output connected but no panel input — check PV fuse and combiner box.
PV voltage normal, charge A = 0: Controller has power but isn't charging — fault code, BMS inhibit, or parameter issue (steps 2–4).
PV voltage normal, charge A normal: System is charging — check whether the battery voltage is actually rising.

Common fault codes: Victron Err 33 (PV over-voltage) and Err 38 or Err 39 (PV input shutdown, where the controller has internally shorted its own PV input to stop charging) — see our Victron MPPT error codes guide. EPsolar Tracer: E01 (battery over-voltage), E02 (battery under-voltage). Renogy: P01 (battery connection fault).

2

Verify the battery charge parameters — absorption and float voltages

Wrong voltage settings are the most common cause of apparent charging failure. Verify these against your battery spec:

Correct charge voltages by battery type
12V LiFePO4: Absorption 14.2–14.6V · Float 13.5–13.8V · No equalization
24V LiFePO4: Absorption 28.4–29.2V · Float 27.0–27.6V
48V LiFePO4: Absorption 56.8–58.4V · Float 53.6–54.4V
12V AGM/GEL: Absorption 14.4–14.8V · Float 13.6–13.8V
12V Flooded LA: Absorption 14.7–15.0V · Float 13.2–13.8V · Equalization 15.5–16.0V

If the battery type selector is set to the wrong chemistry, the controller may complete the charge cycle prematurely (too-low absorption voltage) or overcharge (too-high float). Select a custom or lithium profile and enter the manufacturer's values manually.

3

Check for shading, panel damage, or a blown DC fuse on the PV string

Physically walk the site and inspect the panels and wiring:

• Shading: Even a single shaded cell on a series string reduces total output significantly. Check for new obstructions — tree growth, satellite dishes, aerial cables, bird nests.
• Panel damage: Cracked glass, delamination bubbles, or burnt cell marks (hotspots) reduce output. Check visually from the ground with bright light.
• PV fuse or breaker: Series fuses in combiner boxes can fail silently. Check each fuse with a multimeter on continuity mode. A tripped DC circuit breaker may have reset visually but can still have failed internally — replace if in doubt.
• Open-circuit voltage test: With multimeter on DC voltage, disconnect the PV string at the controller and measure across the positive and negative PV terminals. A 4-panel 12V string should read 75–90V OC in full sun. Below that points to shading, a damaged panel, or a wiring fault.
4

Check for charge inhibit — BMS lockout, low temperature, or deep discharge protection

Lithium batteries actively block charging under certain conditions. This is protective — not a fault:

• Low temperature cutoff: LiFePO4 batteries stop accepting charge below 0°C. The BMS sends a charge inhibit signal to the MPPT controller. Check the battery temperature display or probe. If the battery is in an unheated space during winter, this is the cause — see our cold weather battery guide.
• Deep discharge protection: If battery SoC drops below around 10–15%, the BMS may enter protection mode and lock the battery. Some BMS units require a specific reset — often holding the power button for 5 seconds, or applying a brief external charge. Check the battery manufacturer's manual.
• Cell imbalance: If one cell in the battery is significantly below others, the BMS may prevent charging to protect that cell. This requires battery monitoring or a cell-level voltage check.
• CAN/RS485 inhibit: If the battery communicates via CAN bus or RS485 to the MPPT controller, a communication fault can cause the controller to default to charge inhibit. Check the communication cable and verify the controller shows the battery as communicating.
5

Check firmware compatibility and perform a controlled reset of the MPPT controller

If steps 1–4 have not identified the cause, firmware or a corrupted controller configuration is likely:

• Firmware update history: Check whether the charging problem started after a firmware update to the controller or the battery BMS. A firmware update can change charge algorithm defaults or protocol handling.
• Victron SmartSolar: Open VictronConnect, check firmware version under the device info page. Update via Bluetooth if available. If recently updated, the update history is shown — compare timestamps against when the fault appeared.
• Factory reset: Most MPPT controllers support a factory reset via a settings menu or button combination. This clears any corrupted or conflicting settings. After resetting, re-enter all battery parameters manually from the manufacturer's specification sheet — do not rely on auto-detect for lithium batteries.
• Victron-specific: For Victron systems with a BMS-managed battery, also check the battery BMS disconnect guide and verify DVCC is configured correctly on the Cerbo GX.

Why off-grid charging faults are harder to diagnose than grid-tied faults

Grid-tied hybrid inverters from brands like GivEnergy, Sunsynk, or Lux report detailed fault codes through cloud monitoring portals, making diagnosis straightforward. Off-grid systems are often built from components — an MPPT controller, a separate battery BMS, and loads — that don't share a common monitoring platform. The MPPT controller may only show a two-digit error code. The battery BMS may only communicate via a proprietary app. There is no shared event log.

The good news is that off-grid charging faults are almost always caused by one of the five issues above. In our experience, wrong battery charge parameters and low-temperature charge inhibit account for the majority of cases where an off-grid system appears healthy but won't charge. Actual hardware failure — failed MPPT controller, failed battery cell — is relatively rare and usually accompanied by obvious symptoms like a hot enclosure, burning smell, or visually damaged components.

Related off-grid guides
Brand-specific MPPT guides
FAQ

Off-grid not charging — common questions

The most common reasons are: incorrect battery charge parameters (wrong voltage thresholds for your battery chemistry), a BMS charge inhibit signal from a low-temperature or cell fault, a blown PV fuse or tripped breaker, partial shading on a panel string, or a fault code on the MPPT controller. The controller display or monitoring app will usually identify which applies — check there first before investigating the panels or wiring.
Zero charge current in full sun usually means one of four things: the battery is already at the float voltage and the controller has reduced charging to maintenance level, the BMS has sent a charge inhibit signal, the PV voltage is not reaching the controller (blown fuse, damaged cable, or panel issue), or the controller has a fault condition active. Check the PV input voltage reading on the controller — if it is zero or below battery voltage, the PV side is the problem. If PV voltage is normal but charge current is zero, the issue is on the battery or BMS side.
Compare your controller's absorption voltage setting against your battery specification. For a 12V LiFePO4 battery, absorption should be 14.2–14.6V and float should be 13.5–13.8V. For 24V, double these values. For 48V, quadruple them. If your controller is set to a sealed lead-acid (SLA) profile, the voltage may be too high for lithium cells. Always select a custom or lithium profile and enter the battery manufacturer's exact voltage specifications.
Yes — LiFePO4 batteries should not be charged below 0°C. A properly functioning BMS will block charge current below this threshold. Charging lithium cells at sub-zero temperatures causes lithium plating on the anode, permanently reducing capacity. Lead-acid batteries also charge poorly in cold — their internal resistance increases significantly. If your battery is in an unheated outbuilding, cold-weather charge inhibit is a likely cause of missing or reduced charging during winter.
Winter charging failure typically combines two causes: reduced solar input and low battery temperature. UK peak sun hours drop from 4–5 hours to 1.5–2.5 hours per day in winter, and a low sun angle means horizon obstructions that don't shade panels in summer will shade them in winter. If your battery store is unheated, it may drop below the LiFePO4 charge cutoff temperature. The result is a battery that progressively discharges until the BMS enters deep discharge protection.
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