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Power-Tool 18650 Rebuild Side Quest

A work log for evaluating full-cell replacement in failed 18 V-class power-tool battery packs using new matched high-drain 18650 cells, retained OEM electronics, and spot-welded nickel interconnects.

Initial Packs

• Ryobi ONE+ 18 V 4 Ah pack, expected 5S2P / 10-cell architecture
• DeWalt DCB207 20 V MAX 1.3 Ah pack, 5S1P / 5-cell architecture

Pack History

Ryobi ONE+ 18 V 4 Ah

The pack was opened after the OEM charger would not recover it. The cell array measured approximately 9 V total. Multiple short external charge attempts and repeated OEM charger attempts did not return it to service. The current direction is complete 10-cell replacement while preserving the OEM board, thermistor, terminal assembly, carrier, and usable insulation.

DeWalt DCB207

This pack was previously rebuilt with recycled cells from another project. It returned to service and survived roughly one year of actual tool duty. The next rebuild replaces that exhausted salvage set with five new matched high-drain cells.

Ordered Materials

• 25 BAK N18650COP flat-top cells, 2500 mAh nominal, 30 A listing
• 100 flat-top positive-terminal insulators
• 20 ft of 8 mm x 0.15 mm pure nickel strip

Order total: USD 108.06 shipped and taxed.

Planned Cell Allocation

• 10 cells: Ryobi 5S2P rebuild
• 5 cells: DeWalt 5S1P rebuild
• 10 cells: reserve, weld setup, or later side-quest work

Equipment

• Portable battery spot welder, Amazon ASIN B09V2R1TKD
• Keenstone four-bay charger, Amazon ASIN B07JD77LVD
• Digital multimeter
• IR thermometer
• Kapton tape

Completed Work

• Documented the original cells, pack layouts, series/parallel geometry, and board connections before removal.
• Cut the original interconnects destructively with side snips to separate the exhausted arrays.
• Observed an arc when a cut connection contacted the conductive cell casing, confirming the casing as an active shorting path during teardown.
• Released the original cells from the plastic cages while preserving the reusable pack structures and electronics.
• Desoldered the remaining cut board leads and cleared the connection points with a solder sucker.
• Cut replacement main leads, formed the required angles, and spot-welded the angled interfaces in preparation for final assembly.

Cell Charging

The new cells were charged individually in four-cell lots. Each lot required roughly four hours to reach the charger's full indication, with final displayed voltage near 4.22 V per cell. This establishes a common charged starting condition for assembly; it is not a measured discharge-capacity result.

Charger Role and Limitations

The charger provides independent bays, 4.2 V lithium-ion charging, selectable 500 mA or 1000 mA current, and per-bay voltage, current, and elapsed-time indication. It is suitable for gross incoming-cell screening, but it is not being treated as a calibrated analyzer. It does not provide controlled discharge-capacity testing or verified internal-resistance measurement.

Assembly Assumptions

• Install a positive-terminal insulator on each new cell before laying out nickel.
• Preserve and reuse OEM carriers and insulation where intact.
• Reassess insulation after the original arrays are removed and replacement geometry is known.
• Use 8 mm x 0.15 mm pure nickel, with parallel paths where needed to reproduce effective OEM bus geometry.
• Establish welder settings by destructive peel testing on scrap or retired cells before welding service cells.
• Use soldering only where needed for board tabs, sense leads, thermistor leads, or terminal connections, while avoiding prolonged direct cell heating.

Next Step

1. Reassemble the charged cells in the original Ryobi 5S2P and DeWalt 5S1P configurations.
2. Reinsert each rebuilt array into its plastic pack structure.
3. Verify orientation, group voltages, and total pack voltage before reconnecting electronics.
4. Spot-weld the retained board leads to the new battery interconnects.
5. Perform mechanical, continuity, and thermal checks before first charger insertion.

Pre-Energization Checks

• Verify cell orientation against the original layout.
• Verify every series-group voltage independently.
• Verify monotonic node progression from B- through intermediate taps to B+.
• Verify total pack voltage.
• Check for unintended continuity between nickel and isolated cell-can areas.
• Inspect all welds mechanically and visually.
• Confirm thermistor placement and attachment.
• Confirm no nickel edge can contact a cell shoulder or case under compression.

Initial Success Criteria

DeWalt

• The new 5S1P array is accepted by the OEM charger.
• The pack reaches normal charged voltage.
• The pack operates a representative tool without immediate voltage collapse or abnormal heating.
• Performance materially exceeds the exhausted salvage-cell rebuild.

Ryobi

• The new 5S2P array is accepted by the OEM charger.
• All five parallel groups remain closely matched during the first charge.
• The pack returns to normal tool operation without abnormal heating or early cutoff.

Open Items

• Record the exact Ryobi pack model and original cell markings.
• Record final group voltages and total pack voltages before board reconnection.
• Record exact spot-welder markings and successful settings for 0.15 mm pure nickel.
• Add first-build results, charger acceptance, tool behavior, and thermal observations.

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