Why is my solar battery not charging from the grid?Why is my solar battery not charging from the grid?
Most solar battery advice online is generic. This isn’t. Below is what’s actually happening inside a battery when it misbehaves, backed by degradation research and real installer-reported fault patterns — so you can tell the difference between something trivial and something that needs proper diagnosis.
How a Solar Battery Actually Fails
Every home battery has two separate systems that can go wrong independently: the cells (where energy is stored) and the BMS — Battery Management System (the electronics that protect and balance those cells). Most “battery problems” aren’t the cells at all — they’re the BMS misreading a condition and shutting things down defensively. That distinction matters, because a BMS fault is very often repairable; degraded cells are a different conversation.
“My Battery Isn’t Charging From the Grid”
This is a configuration issue in the large majority of cases, not a hardware fault. Two things commonly cause it:
- The charge schedule falling out of sync with your actual off-peak tariff window after a tariff switch
- The system silently reverting to “self-consumption only” mode after a firmware update, which stops grid charging entirely
Check these before assuming anything’s broken — this alone accounts for a large share of “battery not charging” reports.
Relay Clicking, Then Shutdown
This points to the BMS repeatedly attempting a self-test and failing it — often a control board fault rather than dead cells. Documented cases (SpeakEV forums) show this pattern being resolved by board-level repair, sometimes after weeks of back-and-forth with manufacturer support. Don’t keep power-cycling it — repeated attempts to force a battery through a failed self-test can add cycle stress on top of whatever’s already wrong.
Why Batteries Lose Capacity Over Time — and What’s Normal
This is where most people have no real reference point, so here’s the actual data:
- A widely-cited UK study (Warwick/Birmingham universities with Cenex) found a home lithium-ion battery lost roughly 20% of its capacity over 5 years, with internal resistance nearly doubling — a “tangible” hit to how much energy the battery can actually hold and deliver.
- Manufacturer-published figures vary sharply: Pylontech states around 90% capacity retained after 10 years; Sunsynk’s own published spec puts usable capacity at just 40% by year 10 — a huge difference depending on brand and chemistry.
- Degradation isn’t linear. Lithium batteries follow a “knee curve” — slow, steady loss for years, then an accelerating drop once they pass a certain threshold. This is why a battery that seemed fine last year can suddenly feel noticeably worse.
- Depth of discharge matters a lot: cycling a battery between 5–100% daily can cut lifespan by 30–40% compared to keeping it in a gentler 15–90% range. If your installer never explained this, your battery may be ageing faster than it needs to.
Why this matters for repair vs. replace: a battery reading “low capacity” isn’t automatically dead cells — it might be a BMS that’s become overly conservative, masking real remaining capacity. This is exactly the kind of thing a proper diagnostic can distinguish, and why “it’s just old” is often the wrong conclusion.
Inverter “Forgets” Settings After Using the Isolator
A genuine, if less common, fault: some inverters lose their configuration every time the emergency isolator is used, requiring a full reprogram each time. This is a settings-retention fault at board level — permanently fixable, not something you should have to live with as a quirk of your system.
The Diagnosis-First Approach
Every issue above has the same underlying lesson: symptoms that look identical from the outside (a battery that “isn’t working”) can have completely different causes — configuration, BMS logic, board fault, or genuine cell degradation — and only one of those is actually expensive to fix.
We repair more than 60% of the batteries that come to us, specifically because most faults sit at the BMS or board level rather than in degraded cells. That’s not a marketing number — it reflects how these systems actually fail. Get a diagnostic before you accept “replace it” as the only answer.
