Battery won't charge — repair and rebuild
If the device sees the battery but charging never starts — the charger indicator stays inactive, the device refuses current, or charging stops after a few seconds — the most common causes are a BMS lockout triggered by deep discharge, a failed charge controller IC on the charger or the device's own board, or a single dead cell group whose voltage diverges from the rest and prevents the cycle from completing.
Unlike a battery the device cannot detect at all, here the electrical link is established but current never reaches the cells. That points at the BMS protection, the charging circuit or thermal protection — not at a broken contact or a faulty identification chip.
We diagnose and rebuild lithium-ion batteries for robot vacuums, cordless vacuums, power tools and other battery-powered household devices (we do not work on e-bike or e-scooter packs). Our technicians use laboratory power supplies and oscilloscopes to check each cell's voltage, internal resistance, and BMS protection status. After cell replacement we calibrate the BMS and run a full charge-discharge cycle test to verify proper battery operation. All battery work comes with a 6-month warranty.
A battery that won't charge is one of the most common issues we deal with every day. Many clients assume the battery is completely dead, but in practice it is often enough to replace one cell group or reset the BMS lockout to get the device working again at full capacity. We never recommend buying a new device when the battery can be rebuilt — it is both more economical and more environmentally friendly. Bring the device in — we will inspect it, advise you, and agree on a cost estimate before starting any work.
Likely causes
- BMS lockout — over-discharge protection has activated — The battery management system (BMS) protects cells from excessive discharge. If the device has been stored in a discharged state for an extended period, cell voltage drops below the critical threshold and the BMS blocks any charging attempt. In this case the standard charger cannot start charging because the BMS will not open the current path. We use a lab power supply to restore cell voltage in a controlled manner and reset the BMS protection.
- Charge controller IC failure — The charge controller (charge IC) is a chip that regulates charging current and voltage. After power surges or prolonged use, this chip can burn out or begin operating incorrectly. The charger appears to work but no current reaches the battery. We diagnose the charging circuit with an oscilloscope and replace the failed component.
- One dead cell group preventing the charge cycle — In lithium-ion batteries, cells are connected in groups (series or parallel). If one group has degraded and its voltage differs from the rest by more than 0.5 V, the BMS stops charging because the balance between groups has been violated. The battery shows partial charge but never reaches 100%. The fix is to replace the damaged cell group with new lithium-ion cells.
- Thermal protection — the BMS refuses to charge a too-cold or too-hot pack — Lithium-ion cells can only be charged safely in roughly the 0–45 °C window. If the pack came in from the cold, or has just heated up under heavy load, the BMS thermistor trips and blocks charging until the temperature normalises. A failed thermistor or a lost thermistor contact makes the BMS think the pack is permanently out of range. We test the thermistor resistance and replace it when needed.
- Charging circuit failure on the device motherboard — The battery itself is not always at fault — sometimes the problem lies on the device's own board, where the charge regulator (the device-side charge IC, e.g. inside a laptop or a power-tool body) lives. MOSFET transistors, shunt resistors, or inductors on the board can fail after a short circuit or voltage spike. The battery is healthy but the device simply cannot charge it. In this case we repair the motherboard at the component level.
Try this first
- Try a different charger if one is available — this rules out the charger PSU itself as the cause.
- Clean the battery contacts with a dry cloth or isopropyl alcohol — dust and oxide can block current flow.
- Leave the device connected to the charger for at least 30 minutes — some BMS circuits allow a slow recovery charge (kickstart) that can initiate the cycle.
- Let the battery reach room temperature if it just came in from the cold or is hot from use — thermal protection blocks charging outside the 0–45 °C window.
- Try plugging the charger into a different outlet — sometimes the problem is simply a faulty socket or extension cord.
When to bring it in
If after all these checks the battery still won't charge, bring it to our service centre. It is especially urgent to visit us if the battery is swollen or deformed, if the device emits a burning or chemical smell, or if the battery becomes unusually hot during charging. We diagnose the problem, agree on a cost estimate before starting any work, and provide a 6-month warranty on all battery work.
Battery replacement warranty: 6 months.
Brands we repair
FAQ
Why customers choose SATER
- Custom-built battery assemblies. We design and assemble packs for the exact device — no 'close enough' substitutes.
- Sony, Samsung, LG, Panasonic, Molicel cells. Only top-tier cells — each one capacity-tested before assembly.
- Batteries for robots, power tools, laptops. We build packs for any device that runs on lithium batteries.
- 30+ years of experience. The service centre has been operating since 1993.
- We serve all of Latvia. Electronics service centre in Riga — we accept devices from anywhere in the country.