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Solar Battery Not Charging Or Empty By Morning
The battery sits at a low percentage all day, or fills up and is flat again before breakfast.
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What's happening?
A home battery is not a single device but a set of rules about where energy goes, and most complaints about batteries turn out to be complaints about how those rules were configured. Three separate things decide behaviour. The charging priority: does surplus go to the battery, to the car, or to export, and in what order. The reserve: many systems hold a floor percentage back for backup, so a battery that never goes below a certain level is doing what it was told. And the schedule: batteries on time-of-use arrangements are often set to charge from the grid overnight and discharge across the evening peak, which looks like a fault to anyone expecting solar-only behaviour. Genuine faults do exist — a failed module, a battery management system reporting an error, a hybrid inverter fault taking down both functions — and they usually announce themselves as an error rather than as odd behaviour.
What usually causes it?
- Charge priority set so surplus exports or goes to a car before the battery
- A reserve percentage configured for backup, making the battery look permanently part-full
- A time-of-use schedule charging and discharging at set times, unrelated to the sun
- Not enough surplus in winter to fill the battery at all, which is normal rather than faulty
- Household base load higher than expected, emptying the battery overnight legitimately
- A battery module or battery management system fault reported at the inverter
- A hybrid inverter fault stopping both generation and storage together
Is it dangerous?
A domestic battery is a large amount of stored energy in a sealed enclosure, and it is not a homeowner-serviceable item. Never open a battery enclosure, never disconnect its cabling, and treat any bulging, heat, unusual smell or persistent alarm as urgent — isolate at the point the installer showed you and call them. Batteries also have specific location and fire separation requirements that were assessed at installation, which is one reason relocating one is not a DIY job.
Can I fix it myself?
Read the settings before assuming a fault. In the app, find the charge priority, the reserve or minimum state of charge, and any schedule, and check each against what you thought the system was doing. Compare a sunny summer day with a dull winter one — a battery that fills in June and never fills in December is behaving correctly. Look at your overnight consumption: an immersion, an electric car or storage heating will empty a domestic battery well before morning. Note any error code shown at the inverter or battery.
When should you call a solar installer?
Call the installer for any battery or battery management error code, for a battery that will not charge on a genuinely sunny day with surplus available, for a sudden loss of usable capacity, and for anything physical — heat, noise, smell or swelling. Also call them if the settings do not match the behaviour you were sold, because commissioning a battery correctly is part of the installation.
What will the solar installer actually do?
- Read the battery and inverter logs rather than working from the app summary
- Check charge priority, reserve level and any time-of-use schedule against what the household needs
- Test the battery's usable capacity against its rated figure to identify real degradation
- Diagnose battery management system and module faults, and arrange warranty replacement
- Check the hybrid inverter where generation and storage have failed together
- Confirm the installation still meets the siting and separation requirements it was designed to
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