Home battery not working properly? Revise, repair or replace

First find out what is wrong, then choose. When the settings or the installation are the cause, a revision puts the battery right. When one part fails, such as a module, a fuse or the BMS, a repair is enough. Only when the cells are worn or unsafe is replacement the right step. We connect new batteries, and we also do home battery revision and maintenance, including repairs on battery systems that are already installed.

Maybe this sounds familiar. You own a large home with a heat pump and one or two electric cars. The battery has been in the garage for a few years. Lately it stops at 40% in the evening, or it charges from the grid at night. The app shows an alarm you do not understand. One owner on the Victron forum described it well. "I contacted the installer, who said everything was fine with the system, but I insisted." Another wrote that his battery was "not charging when there is excess solar and also not discharging at night".

What you do not see yet is the real cost. A battery that quietly holds back costs you self-consumption every day, and it may no longer carry the house in a power cut. The obvious fix, a new battery, is often the wrong one. If the cause is a setting or a meter, a new battery behaves exactly the same. And every month you wait eats into the two-year legal guarantee.

Take a look at the home in Lokeren. The solar panels and inverters stayed in place and were combined with a BYD LVS battery of 16 kWh. In Kapellen, the system sends phone alerts, for example when the battery is full or charges from the grid. A problem shows up early.

What are the symptoms of a home battery fault?

A home battery fault shows up as one of a few patterns. It does not charge or discharge, charges from the grid, stops at a fixed level, loses contact, or fails in a power cut.

Each pattern points to a different cause. Match what you see to the row below before you call anyone, and write down when it started.

Why does a home battery not charge?

A home battery that does not charge usually receives the wrong signal, is too cold, or is told by its own BMS to stop. A dead battery is the least likely cause.

The battery system decides when to charge from a meter at your connection. If that meter or its current sensor sits in the wrong place or faces the wrong way, the system thinks you import when you export. This can happen when the switchboard is changed or a solar inverter or charger is added later.

Temperature is the second cause. Many lithium iron phosphate (LFP) batteries may not charge below 0 °C, and the BMS then blocks charging. A common rack battery, the Pylontech US3000C, lists a charging range of 0 to 50 °C and a discharging range of -10 to 50 °C. A battery in a cold garage can discharge in winter but refuse to charge. Our article on placing a home battery outside explains what that means for placement.

The third cause is communication. When the battery and the inverter do not talk to each other, the inverter charges blind or not at all. Victron notes that a lithium battery on a CAN connection can tell the system to stop, and the system then follows the battery.

Why does the battery not discharge, or charge from the grid at night?

Because the control system protects the battery or keeps a reserve. Most of these cases are settings that do what they were told, not faults.

Victron lists the usual reasons why a system refuses to discharge. The state of charge is below the set limit. A CAN-bus battery has set its discharge limit to zero. The switch is on "charger only". Or the inverter still has to run a relay test of about one minute before it may use battery power. In the "keep batteries charged" mode, the battery is only discharged during a grid failure, which is right for back-up and wrong for self-consumption.

Night-time charging from the grid also has a logic. The system recharges automatically when the charge drops 5% or more below the minimum level. A dynamic-price schedule can charge on purpose when power is cheap. If the battery empties and then charges every night, the minimum level is usually set too low for the season.

The best-known effect is BatteryLife, a Victron function. It raises the lower limit by 5% for each day without a good charge. On a day the battery reaches 95%, it lowers the limit by 5%. After a grey week, the battery seems to stop at 35 or 40%. It is not broken: it is waiting for a full charge.

Is it the battery, the settings or the installation? How a diagnosis works

A good diagnosis works from the data to the hardware, so nothing is replaced on a guess. It moves from the cheapest cause to the most expensive one.

Since 18 August 2024, the EU Battery Regulation requires the BMS of a stationary storage battery to hold up-to-date data on its state of health. The person who bought the battery, or a third party acting for them, gets read-only access to that data. The parameters include remaining capacity and, where possible, remaining power, round-trip efficiency, self-discharge and internal resistance. That makes an independent diagnosis possible, also when the original installer is no longer around.

Two numbers from the state of health tell most of the story: the remaining capacity and the difference between cells or modules. Our article on how long a home battery lasts explains what those figures mean over ten years.

Revision, repair or replacement: what is the difference?

Revision restores a battery that works but underperforms. Repair fixes a failed part. Replacement installs a new battery, sometimes with a new inverter.

A revision is the step most owners skip, and the one that most often solves the problem. In Hasselt, for example, the control panel of the battery system was built into the existing electrical cabinet.

Be careful with the word "refurbished". Under the EU Battery Regulation, remanufacturing means taking apart and evaluating all cells and modules. The battery must then reach at least 90% of its original rated capacity. The state of health of the cells may then not differ more than 3% between them. A battery that only got a software reset is not remanufactured.

Can you replace one module, or must the whole battery go?

Often one module or one part can be replaced, as long as the new part matches the old ones. When the rest of the battery is worn, a single new module brings little.

A new module next to modules that are years old works only within the maker's rules. The weakest module sets the pace for the whole string. Our article on expanding a home battery later explains when new and old modules can work together.

Replacement is the better choice in three cases:

• The cells are worn. The state of health is low on all modules, not just on one.
• The battery is physically damaged. Swelling, water, heat marks or a smell mean the battery goes out of service and to a specialist recycler. Our recycling service takes in lithium and home batteries for checking and dismantling. How a home battery is handed in and recycled is explained in what happens to a home battery at the end of its life.
• The house has changed. A heat pump, a second car or a wish for full back-up often needs more power per phase, not only more kWh. Read how big a battery a large home needs first.

Replacing the battery does not mean replacing everything. In Lokeren, the solar panels and inverters were kept and combined with a new battery. Whether your solar inverter can stay is explained in our article on adding a battery to an existing SMA or SolarEdge installation.

Why does the battery no longer take over in a power cut?

Because back-up depends on more than the battery. Island mode, the circuits on the back-up output, the reserve in the battery and the relays must all work.

Three causes come back often. The mode or reserve changed, for example after an update or a new energy contract. Circuits were moved in the switchboard, so the heat pump or the kitchen is no longer behind the battery. Or the battery was empty when the grid failed. With our home battery systems, the takeover happens within 20 milliseconds, but only for the circuits that are connected to the back-up output.

In a three-phase house, check that all three phases are backed up, as in Kortenberg. For long outages, a flat battery needs a way to restart: read how a generator recharges a home battery. Our guide to a home battery with back-up power explains the three levels of back-up. Our article on full no-break wiring shows how the switchboard is built.

Your installer says everything is fine, or is gone: what are your rights?

You have more rights than most owners think. They come from the legal guarantee, the maker's warranty and the EU Battery Regulation.

• Legal guarantee. The seller is liable for a lack of conformity that exists at delivery and appears within two years (Directive 2019/771).
• Repair or replacement is your choice. You may choose between repair and replacement, unless one of them is impossible or costs the seller disproportionately more.
• Repair extends the guarantee. The EU right-to-repair directive adds 12 months, once, to that period when repair is the remedy. Member states apply it from 31 July 2026.
• The maker's warranty runs separately, often on retained capacity over years. Read its conditions in our article on home battery lifetime and warranty.
• The battery data. For newer stationary batteries, you or someone acting for you may read the state-of-health data in the BMS.

"User error" is a common answer, as one owner found out when his installer came, "fiddled with some settings" and later refused the warranty. Ask for the data behind every verdict: the history, the alarms and the state of health. Do not open the battery yourself: our article on installing a home battery yourself explains what the AREI inspector checks.

What changes on paper after a repair or replacement? (Flanders)

In Flanders, Fluvius wants to know about changed modules and new batteries. A new inspection is only mandatory when the electrical installation or the protection changes.

• Replaced modules or a new battery: report it through the Fluvius contact form. Give the number of modules, type and capacity, whether existing modules were replaced, and the date.
• Only extra modules: a new inspection is not mandatory, but Fluvius recommends one for safety.
• A new inverter: re-inspection is not mandatory, unless the installation or the safety switch also changes. A hybrid inverter that drives both panels and battery is reported for both installations separately.
• Battery out of service: you can deactivate it in Mijn Fluvius, and reactivate it later.

In Wallonia and Brussels, you report the change to ORES, RESA or Sibelga under their own rules. Our article on registering a home battery in Belgium explains the procedure per region.

When is repairing a home battery not worth it?

When the battery was never designed for what you now expect from it. Then a revision only makes a small system work as small systems do.

A plug-in battery on a socket will never give full back-up, however well it works. Read what a plug-in battery cannot do. An old off-grid battery bank is a different story too: our article on replacing an old off-grid system covers it. And when the cells are worn on every module, a revision only postpones the replacement. Then it is better to size a new system for the house you live in today.

How do we revise or repair your home battery?

We look at the data first, and we only replace what the data shows is needed. Our team includes three certified battery experts.

1. Step 1: You send us the brand and type of the battery and inverter, the year of installation and screenshots of the app or monitoring.
2. Step 2: We read the history, the settings and the battery data, and check the meter, cables and back-up circuits.
3. Step 3: You get a clear verdict: revision, repair or replacement, and why.
4. Step 4: We carry out the work and test the back-up. Where the change requires it, the installation is inspected and reported to the grid operator.
5. Step 5: You follow production, storage and use in the VRM app and portal, and the system can be monitored and controlled remotely.

We connect almost all inverter types to a home battery, so a new battery does not have to mean a new solar installation. More about our home batteries with back-up.