Safety first (non-negotiable)

If the pack is swollen, leaking, smoking, hot (>50 °C) or smells burnt → DO NOT TEST OR CHARGE. Isolate outdoors on a non-combustible surface and contact a certified recycler or hazardous-waste center.
Work on a non-conductive bench with eye protection and insulated gloves when handling terminals or doing load tests.
Never short a battery. Use insulated leads and rated resistors or an electronic load.
If you’re uncomfortable with electrical measurements or opening packs — stop and use a certified service.

What you’ll need (tools & consumables)

Digital multimeter (DC volts, 20 V or higher range; 10 A range preferred).
Load options (choose one):
- Preferred: adjustable electronic load or power resistor bank rated correctly (see resistor calculation).
- Alternative (practical jobsite): use a real tool under a consistent moderate load (e.g., a drill on light wood) and measure terminal voltage while running.
Stopwatch / phone timer.
Isopropyl alcohol (≥70%) and lint-free cloth for contact cleaning.
Insulated alligator clips / test leads.
Small fireproof tray (ceramic/metal) for temporary isolation.
IR thermometer (optional) to spot hot areas.
Electrical tape for terminal protection when storing defective packs.

Important power / resistor note (do this correctly)

If you want to load an ≈20 V (18V LXT) pack at ~2 A using a resistor, calculate accurately:

Desired current: I = 2.000 A.
Approximate pack voltage: V ≈ 20.00 V.

Resistance:
R = V ÷ I = 20.00 ÷ 2.000 = 10.00 Ω.

Power dissipated:
P = V × I = 20.00 × 2.000 = 40.00 W.
(Equivalently I²×R = 2.000² × 10.00 = 4.000 × 10.00 = 40.00 W.)

Conclusion: Use a resistor rated ≥ 50 W (safety margin). A 10 W resistor is unsafe here. If you don’t have a suitably rated resistor, use an electronic load or a real tool as the load.

Quick 60-second triage (visual + swap checks)

Visual inspection: swelling, cracks, melted plastic, wet/leaking, or heavy corrosion on terminals → Retire pack (do not test).
Charger & outlet: plug the charger into a known-good outlet; observe the charger LED with no battery — some chargers show faults even unloaded.
Swap test: if possible, put a known-good Makita battery into your charger and the suspect battery into a known-good charger. Interpret:
- Known-good charges OK → suspect battery.
- Suspect battery charges OK in another charger → suspect charger.
- Both fail → further tests required.

Typical reference voltages (field guidance)

Manufacturer specs can vary — check the pack label/manual when in doubt. Use these as practical field thresholds.

Makita LXT 18V (Li-ion) — full open-circuit voltage (OCV) typically ≈ 20.0–21.6 V.
- Red flag after attempted full charge: OCV < ~17.0–18.0 V.
Makita CXT 12V (Li-ion) — full OCV typically ≈ 12.4–12.8 V.
- Red flag after charge: OCV < ~10.0–11.0 V.

Step 1 — Clean, reseat & observe charger LED behavior

Unplug charger. Clean battery and charger contacts with isopropyl alcohol and a lint-free cloth; allow to dry.
Reinsert battery firmly (no forcing). Note charger LED patterns (steady red = charging; solid green = full; flashing/error = temp/ID/contact/fault). If available, consult the charger manual for exact LED meanings.
If the charger reports a temperature fault, ensure ambient and pack temperatures are within spec (do not charge below ≈5 °C). Warm the pack safely (see warming tips below).

Step 2 — Measure open-circuit voltage (OCV)

Set multimeter to DC volts (≥ 20 V range for 18V packs).
Place meter probes on pack terminals and record OCV to two decimals (example: 20.04 V).
Interpret:
- OCV near full band → pack superficially accepts charge.
- OCV significantly low (e.g., < ~17–18 V for 18V packs) → deep discharge, BMS lockout or cell failure likely.

Step 3 — BMS “wake” / recovery attempt (safe first recovery)

Some packs enter protective lockout after deep discharge. Try this sequence:

Put the pack on the charger for 10–30 minutes — many chargers attempt a wake cycle for protected packs.
If no change, install the pack in a compatible Makita tool and run a light, continuous unloaded task until the tool cuts out (this can sometimes bleed a small current and reset the BMS). Stop at cut-off. Rest the pack 30–60 minutes and retry charging.
If charger then accepts it, monitor the next 1–3 cycles for excessive heat or odd behavior. If recovery fails → proceed to electrical tests.

Important: Do not attempt to bypass the BMS with ad-hoc wiring or applying external high voltage. That is dangerous.

Step 4 — Under-load voltage test (health check & internal resistance)

Prefer using a real tool under consistent moderate load. If using a resistor, use the properly rated resistor calculated earlier.

Procedure (example using a 10.00 Ω, 50 W resistor on an 18V pack)

Record OCV first: OCV = 20.00 V.
Connect the 10.00 Ω resistor across the pack terminals using insulated clips. Immediately measure the voltage under load — call this V_load (example 18.20 V).
Estimate current: I ≈ OCV ÷ R.
- OCV = 20.00 V.
- R = 10.00 Ω.
- I = 20.00 ÷ 10.00 = 2.000 A.
Compute voltage drop: ΔV = OCV − V_load = 20.00 − 18.20 = 1.80 V.
Estimate internal resistance: R_internal ≈ ΔV ÷ I.
- ΔV = 1.80 V.
- I = 2.000 A.
- R_internal = 1.80 ÷ 2.000 = 0.900 Ω.

Interpretation — rules of thumb

Healthy: sag ≤ ~1.0 V under ~2 A → low internal resistance.
Marginal: sag ~1.0–2.0 V → aging pack, reduced performance.
Failing: sag > ~2.0 V, or voltage collapses toward tool cutoff → replace the pack.

For CXT 12V packs use the same method but pick a resistor that produces a reasonable current and power (recalculate R & power).

Step 5 — Simple field capacity estimate

With a stable load (resistor or tool), time how long the pack runs until tool cut-off or voltage drops below the working point. Record minutes.
Convert minutes to hours: time_h = minutes ÷ 60. (Compute digits.)
Estimated capacity (Ah) ≈ I (A) × time_h (h).

Worked example (digit-by-digit):

I = 2.000 A.
Measured run time = 45 minutes.
time_h = 45 ÷ 60 = 0.75 h.
Ah = 2.000 × 0.75 = 1.500 Ah.

If the pack is rated 3.0 Ah and you measured 1.500 Ah = 50% of rated → plan replacement.

This is a rough field method. Lab capacity testers are required for exact Ah figures.

Step 6 — Charger output & isolation test

Swap test: known-good battery in charger, suspect battery in known-good charger — still the fastest check.
If you must measure charger output (only if the charger manual provides safe test points): measure DC output with meter (no battery). Expect approximate pack full voltage or the value specified on the charger label. If no output or wildly off → replace charger.
If charger works with known-good packs but rejects suspect pack → battery fault.

Step 7 — Advanced (cell / BMS checks — for experienced technicians only)

Only open a pack if it’s out of warranty and you have the proper tools and safety procedures.
Measure each cell or parallel group: at the same SOC cell voltages should be within 0.05–0.10 V. Larger spreads indicate imbalance or failing cells.
Inspect the BMS PCB for cracked solder joints, burned components, or blown polyfuse. Replacing cells or BMS requires matched Grade-A cells, spot-welding skill and proper testing.
If unsure — stop and replace the pack.

Signs temperature or damage caused permanent harm

Charger continues to reject the pack after warming and cleaning.
Pack gets hot while charging (>45–50 °C) or during light load.
Much shorter runtime even after a verified full charge.
Physical swelling, hissing, or burnt odor.

If any of the above appears → retire and recycle the pack.

Field troubleshooting & quick fixes (ordered)

Clean terminals with isopropyl alcohol and dry.
Try a different outlet and a different charger.
Warm a cold pack to room temp (pocket or insulated pouch) — do not use open flame or direct heating.
Attempt BMS wake (charger 10–30 minutes or tool run as described).
Load test and capacity estimate.
Quarantine packs that fail tests and tape terminals.

Disposal & quarantine procedure

Tape terminals with non-conductive tape.
Label: DEFECTIVE — DO NOT USE, include date and observed symptoms.
Transport in a non-conductive container to a certified battery recycler, retailer take-back, or municipal hazardous-waste facility. Do not throw in household trash.

Decision matrix — replace vs repair

Replace immediately if: swelling, leak, smoke, burning smell, heat while charging after warm-up, OCV very low after recovery (< ~17 V for 18V), sag > 2 V under modest load, or capacity < ~50–60% of rated.
Consider repair (advanced) only if: you can replace one or two cells with matched Grade-A cells and also replace/test the BMS properly. For most users and fleets, replacement is safer and often cheaper in total cost of ownership.

Example — full digit-by-digit worked example (18V pack)

OCV measured = 20.00 V.
Use 10.00 Ω resistor (50 W rated). Calculate current:
- I = 20.00 ÷ 10.00 = 2.000 A.
V_load measured under resistor = 18.20 V. Voltage drop:
- ΔV = 20.00 − 18.20 = 1.80 V.
R_internal = ΔV ÷ I = 1.80 ÷ 2.000 = 0.900 Ω.
If tool ran 45 minutes until cut-off: time_h = 45 ÷ 60 = 0.75 h. Capacity:
- Ah = 2.000 × 0.75 = 1.500 Ah.
If pack rated 3.0 Ah → measured 1.5 Ah = 50% → plan replacement.

Practical tips & jobsite best practices

Prefer using a real tool as a load (often safer and more representative than low-wattage resistors).
Keep at least one warmed spare in an insulated pouch for cold jobs.
Avoid repeatedly fast-charging a hot/warm pack — allow cool-downs between cycles.
Track pack age and retire marginal packs proactively.
Use an IR thermometer to quickly detect hotspots.

FAQ (short)

Q: Why does my Makita charger blink red then green?
A: Often a temperature fault — battery too cold or too hot. Let it return to room temp and retry.

Q: Can a bad charger ruin my Makita batteries?
A: Yes. A malfunctioning charger can improperly charge or fail to terminate charging, shortening battery life or causing damage.

Q: How long do Makita batteries last?
A: With proper care, expect ~3–5 years or roughly 500–1,000 cycles depending on use and environment.

Final notes

Start with the simplest, safest checks (visual, clean contacts, swap test). Use OCV, a short under-load sag test and a basic capacity estimate to decide if a pack is worth salvaging. When in doubt — prioritize safety: quarantine defective packs and replace rather than risk a hazardous failure.

Makita Battery Not Charging — Step-By-Step Fixes