Identify Bad Craftsman 20V Batteries or Chargers Safely

Immediate red flags — unplug & isolate if seen

If any of these appear, stop work immediately and isolate the equipment.

Charger extremely hot, burning/plastic smell, smoke, or loud unusual noise → UNPLUG & ISOLATE.
Circuit or charger fuse trips when battery inserted → UNPLUG & ISOLATE.
Charger shows persistent error LEDs only with this battery (other batteries OK) → STOP CHARGING.
Battery swells, hisses, emits odor, or becomes very hot during charging/use → REMOVE, TAPE TERMINALS & ISOLATE.

Safety priority: when in doubt, treat the pack as hazardous — tape terminals, place in a non-combustible container, and contact your recycler.

3–5 minute isolation checks (jobbox swap & visual)

Run these ordered checks to isolate charger vs battery quickly.

Swap test A: Put a known-good battery on the suspect charger — does the charger behave normally?
Swap test B: Put suspect battery on a known-good charger — does it fault or overheat?
Visual inspection: swelling, cracks, melted plastic, corrosion, or residue around terminals?
Contact cleaning: wipe battery & charger terminals with 70%+ isopropyl alcohol, dry, reseat once.
If suspect battery still faults after swaps → treat battery as defective.

Immediate actions for a confirmed defective battery

Steps to make a defective pack safe for transport/disposal.

Unplug the charger.
Tape terminals with electrical tape and label DEFECTIVE — DO NOT USE.
If the pack is hot or smoking, move it (with insulated tools/gloves) to a non-combustible area (metal tray/concrete) and ventilate.
Deliver to a certified battery recycling/collection point — do not dispose in household trash.

Fast replace vs repair heuristics (field decision)

Use these quick heuristics to decide next action without long bench work.

Charger works with other batteries → Replace the battery.
Suspect battery trips multiple chargers or overheats on a known-good charger → Retire the battery.
Charger faults with multiple known-good batteries, smells, or overheats → Replace the charger.
If repair cost (PCB + labor) ≥ ~70% of replacement cost → Replace instead of repair.

Preventive jobbox practices to reduce failures

Use manufacturer-recommended chargers only. Smart chargers often protect both charger and pack.
Clean contacts monthly and store packs at ~30–50% SOC; avoid extreme heat.
Rotate packs in heavy-use fleets to avoid single-pack overuse and thermal accumulation.
Keep a labeled fallback set of known-good batteries and one spare charger.

Multimeter & Load Test Script — Field Procedure

Safety: Wear eye protection and insulated gloves. Work on a non-conductive surface. Do not open packs. Do not short terminals. If the pack is swollen, leaky, hot, or smoking — stop and follow disposal steps.

for Craftsman 20V CMCCS/CMCCSP Power Tools Battery — CRA-20V-LI Lithium-Ion Battery For Craftsman CMCCS/CMCCSP Power Tools

Prepare before testing

Tools: digital multimeter (0–30 V DC), insulated leads, optional clamp meter, 10 Ω 10 W resistor and insulated clips (for consistent load), stopwatch/phone, notebook.
Known-good charger and known-good battery (if available) speed isolation.
Clear the bench of flammables; keep a metal tray or concrete block nearby for isolating hot packs.

Visual & LED check (no power)

Inspect charger and suspect battery for physical damage, residue, or corrosion.
Insert suspect battery on charger and observe LEDs for 10–20 seconds. Note pattern.
- Normal: steady charge indication per manual.
- Fault: alternating red/green, fast blink, or no light → note and proceed to swap tests.

Swap tests (definitive quick isolation)

Known-good battery → suspect charger: If charger faults with the known-good battery, charger is suspect.
Suspect battery → known-good charger: If good charger faults with the suspect pack, the battery is defective.

Document which combination failed — this is your primary evidence for replace/repair.

OCV measurement (open-circuit voltage)

Ensure battery has been tried on charger or has rested 10–20 min after charging attempt.
Set DMM to DC volts and measure across the pack terminals (no load).
- Expected (Craftsman 20V Li-ion): ~21.0–21.6 V when fully charged.
- Red flag: OCV < ~15–17 V after charging attempts → deep discharge / internal short / BMS lock.

Record OCV value in log.

Charger output spot-check (only if accessible)

Only do this if the charger exposes DC output pins and the manufacturer permits testing.

Power the charger (no battery). Measure DC output at charger terminals.
Compare to the labelled output. If zero or wildly off-spec → charger defective.

Note: Many smart chargers only drive voltage after handshake, so behavior differs with/without a pack — do swaps if unsure.

Under-load behavior (tool load or resistor load)

Option A — Tool as load (quick & safe):

Insert battery into the tool. Run an unloaded or low-torque function for 10–20 s. Measure terminal voltage while running. Observe for stutter, heat, or protection trips.

Option B — Resistor load (repeatable):

Clip a 10 Ω, 10 W resistor across terminals with insulated clips (approx 2 A draw).
Immediately measure V_load and time for 30–60 s. Remove load after test.
Calculate sag: ΔV = OCV − V_load.

Interpretation (use these jobbox thresholds):

ΔV (OCV − V_load)	Action
≤ 1.0 V	Pass — battery can supply ~2 A reliably
1.0–2.0 V	Marginal — schedule replacement / monitor
> 2.0 V or voltage collapse	Fail — retire and replace battery

If the battery heats rapidly during load → replace.

Charger behavior during charging (observe)

Place suspect battery on charger and time first 5–15 minutes. Watch for: case heating (>45–50 °C), constant fan, smell, or tripping breaker.
If the charger behaves normally with other batteries but overheats with the suspect battery → battery is damaging charger — isolate & retire the battery.

Final isolation & action steps

Battery defective: label, tape terminals, place in non-combustible container, recycle at certified center.
Charger defective: remove from service, tag, and replace.
If uncertain: document serials, photos, and swap-test results; escalate to warranty or authorized service.

Compact logging template

Date: ___________   Technician: ___________

Battery model & serial: _______________________
Charger model: _______________________________

OCV (V): ________
V_load (V) under ~2A: ________
Sag (V): ________   (OCV − V_load)

Charger no-load output (V): ________
Observed heat / smell / fault codes: _______________________

Swap tests:
- Known-good battery on suspect charger → (OK / Fault) _______
- Suspect battery on known-good charger → (OK / Fault) _______

Decision: Replace battery / Replace charger / Further service
Notes/actions: ____________________________________________

One-line jobcard workflow

JOBCARD: Visual check → swap tests → OCV measurement → 10 Ω load test → log results → replace if OCV <15–17V or sag >2V or pack causes charger faults.

Quick reference sag table (printable)

Condition	ΔV threshold	Immediate action
Healthy	ΔV ≤ 1.0 V	Return to service
Marginal	1.0 < ΔV ≤ 2.0 V	Monitor; schedule replacement
Failed	ΔV > 2.0 V	Retire & recycle pack

Closing notes (best practice)

Keep a rotation of known-good batteries and at least one spare charger in the jobbox.
Standardize fleet chargers and battery families to reduce cross-compatibility risk.
For repeated failures, log patterns (batch numbers, supplier) — a recurring defect often indicates a bad cell lot or counterfeit cells.
When in doubt about opening or rebuilding, prefer replacement or an authorized rebuild service — safety and liability matter.

Signs Your Craftsman 20V Battery Is Damaging Your Charger