How to Safely Revive a Deeply Discharged Ryobi ONE+ 18 V Battery

Quick TL;DR

Measure the pack OCV, run the low-risk ordered wake steps (OEM charger wake → alternate charger → light tool wake → warm if cold), monitor temperature, then run a controlled load/sag test. If OCV stays below ~17–18 V or pack shows heat, odor, swelling, or >2 V sag, do not continue — send to a qualified service or recycle.

1 — What “deeply discharged” looks like

Measure Open-Circuit Voltage (OCV) with a DC multimeter before attempting any recovery.

OCV (V)	Meaning	Action
20.0–21.6	Full / near-full	Normal operation / charge as usual
18.0–20.0	OK / usable	Charge and test under load
~17.0–18.0	Red flag / likely BMS trip	Attempt safe wake steps; monitor closely
10.0–12.0	Severe deep discharge	High risk — do not force-charge; escalate
<10.0	Very severe / probable internal failure	Quarantine & recycle/repair only by pros

These are practical field bands for a nominal 5-cell (≈18 V) pack — not manufacturer specs. Use them as decision thresholds only.

2 — Tools & safety prep

Minimum kit

Digital multimeter (DC, 20–30 V range)
OEM Ryobi charger(s) (genuine recommended)
A verified “golden” known-good battery and charger for swaps
Isopropyl alcohol + lint-free wipes + soft brush (for external contact cleaning)
IR thermometer (optional, recommended)
Safety PPE: insulated gloves, eye protection
Non-combustible workbench area and a Class ABC/BC fire extinguisher nearby

Workspace rules

Work on a non-conductive, non-combustible surface.
Keep bystanders away.
Log serial number, OCV, ambient temp, and time-stamps for every attempt.

3 — 60-second rapid triage

Visual check: swelling, cracks, discoloration, leaking? → QUARANTINE.
Insert in OEM charger: watch LED patterns for the first 1–5 minutes (temp-wait/charge/err).
Verify power: confirm outlet & charger work by charging a known-good battery.
Swap test: put suspect pack in another known-good charger; put known-good pack in suspect charger. Record outcomes.

This isolates charger vs battery quickly and safely.

4 — Clean contacts & reseat

Power off and remove pack.
Use isopropyl and a lint-free wipe to clean metal rails/contacts; brush debris from the slot.
Dry and firmly reseat. Poor contact often mimics dead packs.

for Ryobi 18V Battery — 18V Lithium Ion Battery Replacement for Ryobi ONE+ Cordless Tools P108 P192

5 — Measure OCV properly

Set meter to DC volts (20–30 V range).
Touch red to positive, black to negative terminals; wait 3–5 seconds for stabilization.
Record OCV, ambient temp, and pack SN. Use OCV table above to decide next steps.

6 — Safe BMS “wake” sequence

Important: follow in order. Stop immediately if pack heats, smells, emits smoke, or swells.

Charger-wake (10–30 minutes)
- Insert into a genuine Ryobi charger and leave for 10–30 minutes. Many chargers apply a small trickle or monitoring charge to wake a protective BMS. Monitor pack surface temp (IR or by touch with glove).
Try another OEM charger or another charger slot
- If you have access to a different genuine Ryobi charger model or slot, try it — firmware/hardware differences sometimes succeed where one charger doesn’t.
Tool-wake (short, light pulses 10–20 s)
- Insert pack into a non-high-load tool (e.g., driver set to low) and give short light trigger pulses to wake BMS. Don’t apply heavy loads. Monitor temp.
Warm the pack (if cold)
- If pack is below ≈5 °C, bring it to room temp or warm vehicle compartment for 30–60 minutes, then retry charger-wake. Do not use direct heat sources (hair dryer, oven, open flame).

If any step produces rapid heating (>50 °C), strong odor, smoke, or swelling, immediately unplug/stop and quarantine the pack.

7 — When to stop and escalate

OCV remains < ~17–18 V after safe attempts.
Pack surface temp rises rapidly or exceeds ~50 °C.
Any burning smell, smoke, or visible deformation.
In these cases: do not attempt force-charging. Photograph, log OCV and attempted steps, tag “QUARANTINED”, and send to a qualified recycler or certified repair center.

8 — Advanced revival (technician-only, do NOT DIY)

Qualified technicians may use a bench DC power supply with strict current-limiting to slowly precharge a cell group at very low current (typical initial <100–200 mA) while continuously monitoring temperature and cell voltages. This is a lab-only technique requiring thermal cameras, isolation transformers, fire suppression, and trained staff. It is NOT safe for untrained users.

9 — Verifying usable capacity after a successful wake

If the pack wakes and charges normally:

Fully charge using OEM charger.
Run a short load/sag test: operate a representative tool or apply an electronic load for 10–20 seconds and record voltage drop.
- Healthy: ≤ ~1 V sag under typical light/medium load.
- Borderline: ~1–2 V sag — monitor and consider retiring for critical work.
- Failing: > ~2 V sag or immediate tool cutout — retire/replace.
Cycle monitoring: run several charge/discharge cycles and log delivered runtime & max surface temp. If capacity or DCIR degrades quickly, plan replacement.

10 — Repair vs Replace vs Recycle

Replace immediately if: swelling, persistent OCV < ~17–18 V after safe wake steps, >2 V sag, hotspots, or odors.
Consider professional repair only if diagnostics point to an isolated, fixable BMS or single-cell issue and repair cost < ~50% of new pack price — performed by accredited service centers.
Recycle any pack declared unsafe or non-recoverable — use certified recyclers, follow local hazardous-waste rules.

11 — Prevent deep discharge: fleet & storage best practices

Store at ~30–50% SOC for long-term storage.
Rotate spares frequently and log usage.
Check stored pack voltages every 3–6 months and recharge to mid SOC if needed.
Avoid leaving packs fully discharged for months and keep packs out of extreme cold/freezing.
Use manufacturer-recommended chargers and avoid cheap unverified chargers.

12 — Absolute DO NOTs

Do not open or puncture packs.
Do not connect packs directly to other batteries (no “jumping” or parallel linking).
Do not force-charge with improvised supplies unless you are a qualified lab technician.
Do not ignore heat, smells, or swelling — always quarantine.

13 — Short FAQ

Q: Can I “jump” a dead Ryobi battery with another battery?
A: Never. Directly connecting packs is dangerous and can cause fire.

Q: How long should I try waking a pack?
A: Follow the ordered low-risk steps; if no safe improvement and OCV sits in the red zone, stop and escalate.

Q: Will a revived pack be as good as new?
A: Usually not. Deep discharge often causes irreversible capacity loss. Treat revived packs as degraded and use them in non-critical roles if retained.

Q: Is it economical to repair packs myself?
A: No — repairs require professional equipment and expertise; for fleets, compare repair cost vs new pack price and safety impact.

14 — Final notes & responsible practice

Reviving deeply discharged Li-ion tool packs is a last-resort operation. Safety comes first: never bypass protection circuitry, never improvise, and log everything. For fleets, standardize the wake/triage process, keep spare validated packs, and favor replacement over risky repair when in doubt. People and property safety is always worth the replacement cost.