Solar battery not charging
Battery sitting at the same state of charge. Not charging overnight on cheap rate. Not filling up from solar. This is one of the most common faults we diagnose — and in the majority of cases it is a settings or CT clamp issue, not a battery hardware failure.
Work through the checks below in order. Most cases are resolved without an engineer.
A remote diagnostic session reviews your portal data live, confirms the cause, and tells you exactly what needs changing — or whether hardware intervention is needed.
Book a Remote Diagnostic — from £75 → What's includedWhat actually stops a battery charging
In order of how commonly we see each cause.
By far the most common cause. Firmware updates frequently reset Timed Charge back to Eco Mode without warning. In Eco Mode the battery will not draw from the grid on a schedule.
A reversed CT clamp makes the inverter see import as export — so it suppresses charging because it thinks the house is already exporting. See CT clamp installed wrong.
The charge window times are incorrectly set, or the inverter clock/timezone is wrong — causing the window to run outside your cheap-rate period.
The battery's operating range maximum is set below 100% — often deliberately at 80% by the installer. The battery stops charging at that level even during Timed Charge.
A firmware update silently wiped system mode, charge windows, and operating range settings. You need to re-enter them all and verify they have saved.
Less common. Shows as a fault code in the event log or an alarm on the battery unit itself. Requires engineer involvement. Rule out settings causes first.
Step-by-step diagnostic
Work through these in order — most cases are resolved before step 5.
Open your portal or app and find the system mode setting. If it says Eco Mode, Self-Consumption, or similar, it will not grid-charge on a schedule. Change it to Timed Charge, Time of Use, or the equivalent for your brand. Save the setting and verify it has stuck by checking back in the app after a few minutes.
Confirm the charge start and end times match your cheap-rate electricity period exactly. Check the inverter clock — if it is showing the wrong time, or is set to UTC when BST is in effect, the window will be running one hour out of phase with your tariff.
Example: Octopus Go cheap rate is 00:30–04:30. If your inverter shows UTC and the UK is on BST (UTC+1), you need to set the window to 23:30–03:30 to match — or switch the inverter clock to local time.
Find the operating range or SoC target setting. Check what the maximum is — if it is set to 80% and the battery is currently at 78–80%, it will not charge any further. The battery is working correctly; it is just following the configured limit. Raise the maximum if you want more charge capacity.
Turn on a kettle and watch the grid import reading in your portal. It should rise by about 2,000–3,000W. If the figure falls, stays flat, or moves in the wrong direction, the CT clamp is reversed — the inverter cannot correctly see grid import and is blocking the charge command. Use the CT clamp installed wrong page for the full fix guide.
Open the event log in your portal and look for any battery-side errors — BMS fault, cell voltage alarm, communication fault, or similar. If you find fault codes, note them down. These usually indicate a hardware issue that requires an engineer rather than a settings fix. A remote diagnostic session can assess the fault codes and advise on next steps.
Battery not charging from solar specifically
If the battery charges from the grid but not from solar, the issue is more likely to be one of these:
Export limiting set too aggressively. If your DNO export limit is set to 0W, the inverter may be curtailing solar before it reaches the battery. Check the export limit setting in your configuration.
CT clamp on the solar circuit is reversed. On installations where the CT monitors the solar feed rather than the grid feed, a backwards clamp shows negative generation — the inverter doesn't see any solar to divert to the battery.
Generation figures look correct but battery still doesn't charge. This can indicate a DC-side connection issue between the solar strings and the inverter's battery charge circuit. Requires on-site investigation.
Frequently asked questions
The most common causes are: system mode is Eco Mode instead of Timed Charge; the charge window times are wrong or out of phase with your tariff; a firmware update reset the settings; the CT clamp is reversed; or the battery's SoC limit has been reached. Check in this order.
Eco Mode tells the battery to charge only from solar surplus and not to draw from the grid on a schedule. It is fine for self-consumption setups but does not support cheap-rate overnight charging. For that you need Timed Charge or Time of Use mode.
Multiple brands including GivEnergy, Growatt, and Sunsynk have firmware histories that include silent system mode resets. The update completes and reverts to Eco Mode, clearing charge schedules. Re-enter your system mode and charge window settings, save them, and verify they are still present the following morning.
Some installers deliberately cap the operating range at 80% to extend battery longevity. This is technically valid but should have been explained at installation. You can raise this limit yourself in the system mode settings — check the operating range slider and set the maximum to your preferred level.
BMS faults are less common than settings issues but do occur. They usually show as fault codes in the portal event log or as a warning light on the battery. Check the event log for battery-side errors. If you find fault codes, a remote diagnostic session can assess what they mean and whether you need an engineer.
If the battery is actively discharging overnight rather than just not charging, the most likely causes are: the system mode has the battery set to supply house loads from storage (which it should not do at cheap-rate times if Timed Charge is configured); or a reversed CT clamp is causing the system to think the house is exporting and triggering discharge in response. Check the CT clamp first.
Still not charging after working through this?
A remote diagnostic includes a live review of your portal data — system mode, event log, charge history, and CT clamp verification. We confirm the exact cause and advise whether it's a settings fix or an engineer visit.