Power Tool Battery Not Charging — Makita, Bosch, DeWalt Troubleshooting

You place the battery on the charger, and instead of the familiar green indication, you see a flashing red light, red-green alternation, or no reaction at all. You need the tool right now, but the battery refuses to charge. Sound familiar?

At the SATER service centre on Silmaču iela 6, we've been repairing power tool batteries for over 30 years. Thousands of Makita, Bosch, DeWalt, Milwaukee, and Hilti packs have passed through our hands. Let's examine the most common reasons why a battery won't charge and how to distinguish a battery fault from a charger fault.

Reading the Charger LED Codes

Makita (LXT 18V, XGT 40V Series)

Makita chargers DC18RC, DC18RD, DC40RA use colour indication:

• Solid red — charging in progress. All normal.
• Solid green — charging complete, battery full.
• Red-green alternating — temperature protection. Battery too hot (above 50°C) or too cold (below -10°C). Charging will begin automatically once the temperature enters the acceptable range.
• Rapid red flashing — error detected. The BMS has identified a fault: one or more cells have abnormal voltage (too low or too high), an open circuit, or internal short.
• Nothing lit — check the charger is plugged in and making proper contact with the battery.

Bosch (Professional 18V, ProCORE)

• 3 LEDs fill sequentially — charging in progress, indicating level.
• All 3 LEDs solid — charging complete.
• All 3 LEDs flashing — temperature protection.
• LEDs flash alternately / erratically — battery error. BMS has rejected the charge due to a faulty cell.

DeWalt (20V MAX, FLEXVOLT 60V)

• Single LED flashing — charging in progress.
• All LEDs solid — battery charged.
• Rapid flashing — error. Hot/cold battery or cell fault.
• Solid red LED + beep — faulty cell detected, charging blocked. Repair or replacement needed.

Milwaukee (M18, M12)

• Sequential indicator fill — charging in progress.
• Flashing red/amber — temperature error.
• Rapid red flashing — cell failure or open circuit. Charging impossible.

Main Causes: Why the Battery Won't Charge

1. Temperature Protection (Too Hot or Too Cold)

The most common cause — and the most benign. Lithium-ion batteries cannot be charged below 0°C or above 45–50°C. The BMS blocks charging to protect the cells.

When this happens: after intensive work (grinding, drilling concrete, sawing), the battery heats to 50–60°C. Or in winter, when the battery has been stored in an unheated garage or car.

Solution: let the battery cool down (30–60 minutes indoors) or warm up (bring indoors for an hour). Temperature protection will disengage automatically.

2. Deep Discharge — the Battery Has "Gone to Sleep"

If a lithium-ion battery has sat unused for several months, cells can discharge below the minimum permissible voltage (typically 2.5 V per cell). The BMS shuts the battery down completely, and the charger cannot "see" it.

Signs: the charger shows no reaction at all when the battery is inserted. No indicators on the battery. The tool won't switch on.

Solution: bring the battery to us. We test each cell individually and can "wake" the battery if the cells haven't degraded irreversibly.

3. Cell Imbalance

In a power tool battery pack, 5–10 cells are connected in series. Over time, some degrade faster than others. The BMS sees one cell at 4.2 V (full) whilst another is at 3.6 V (half empty), and stops charging to prevent overcharging the first.

Signs: battery "charges" quickly (15–20 minutes instead of the usual hour), but runtime is just 5–10 minutes.

Solution: rebuild with replacement of degraded cells. All cells in the pack must match in capacity and internal resistance.

4. One or More "Dead" Cells

A cell can fail completely: internal open circuit, irreversible deep discharge, or internal short. The BMS detects a cell with zero or abnormal voltage and blocks the entire pack.

Solution: replacement of the faulty cell. In practice, if one cell has died, the rest are usually significantly worn too — we typically replace the full set.

5. Dirty Contacts

Dust, grime, and oxide on the battery or charger contacts can disrupt the electrical connection.

Solution: clean contacts with a cotton bud dampened with isopropyl alcohol, or a pencil eraser for removing oxide. Don't use sandpaper — it leaves abrasive particles.

6. Charger Fault

Before blaming the battery, check the charger. Insert a different (known-good) battery. If it also won't charge, the problem is the charger.

NiCd vs Li-ion: the Outdated "Memory Effect"

If you have an older power tool with nickel-cadmium (NiCd) batteries, you may have encountered the "memory effect." Lithium-ion batteries have no memory effect. You can (and should) charge them at any level. Fully discharging a Li-ion battery is harmful — it accelerates degradation.

Attempts to "Revive" a Battery

Doesn't work:

• Freezing. Putting a battery in the freezer is pointless and dangerous.
• Jumpstarting from a car battery. Applying high current without voltage control is a direct route to fire.
• Training cycles. Repeated full charge-discharge doesn't restore Li-ion cell capacity.

May work (but only at a service centre):

• Waking a deeply discharged battery — carefully applying minimal current to each cell individually to raise voltage.
• Replacing a single "dead" cell — if the remaining cells are in acceptable condition.

When a Rebuild Makes Sense

Rebuild is worthwhile:

• Original battery packs are expensive (Makita BL1860: €80–120, Hilti: more)
• The tool is professional-grade and in good condition
• You want increased capacity (can install higher-capacity cells)

Better to buy new:

• Budget tool where a new battery costs €20–30
• Battery housing is damaged (cracks, broken clips)
• BMS is faulty (BMS repair can cost more than a new pack)

Battery Rebuilds at SATER

We rebuild power tool batteries with quality cells: Sony/Murata, Samsung, Molicel, LG, Panasonic. Spot welding (not soldering), each cell tested for capacity and internal resistance before assembly.

We work with all major brands: Makita, Bosch, DeWalt, Milwaukee, Hilti, Metabo, Festool, AEG.

The SATER service centre — over 30 years in Riga, Silmaču iela 6. 186 Google reviews, 4.3★ rating.