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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+ PBP005 18 V 4 Ah

This pack was purchased as a Ryobi reconditioned battery and completed roughly two summers of mowing duty before failing. 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 exhausted salvage set has now been replaced with five new matched high-drain cells. Because the replacement array is 5S1P, the 2500 mAh cell rating carries through as a nominal pack capacity of 2.5 Ah; the series connection increases voltage but does not add amp-hours. Compared with the original 1.3 Ah rating, this is an increase of about 92 percent, nearly doubling the nominal capacity in the same pack format.

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
• 0.15 mm x 27 mm pure nickel 2P H-strip, Amazon ASIN B07VMGTVL5, used for Ryobi cross-row bus fabrication

Order total: USD 108.06 shipped and taxed.

Planned Cell Allocation

• 10 cells: Ryobi 5S2P rebuild
• 5 cells: DeWalt 5S1P rebuild
• 10 cells: reserve for weld setup, another pack, 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
• USB power meter and selectable high-load resistor board

Charger Role and Incoming-Cell Screening

The Keenstone charger provides four independent bays, 4.2 V lithium-ion charging, selectable 500 mA or 1000 mA charge current, and per-bay indication of voltage, current, and elapsed time. It was used for comparative incoming-cell screening rather than as a calibrated analyzer; it does not provide a controlled discharge-capacity test or verified internal-resistance measurement.

The initial screening process was intended to reject gross outliers and included:

• Inspecting each cell for can damage, cap deformation, wrap damage, contamination, or corrosion.
• Measuring incoming open-circuit voltage with the same meter.
• Charging cells under a common 500 mA setting for the initial qualification pass.
• Checking relative case temperature during charging.
• Recording final indicated voltage and approximate charge time.
• Allowing charged cells to rest and comparing rested voltage.
• Rechecking after 24 to 48 hours when practical to identify gross self-discharge outliers.
• Selecting the closest-behaving cells from the same new batch for each pack.

This screening was not represented as calibrated capacity testing or impedance binning.

Completed Teardown and Preparation

• Opened both packs and documented the original cell types, mechanical layouts, series/parallel arrangements, board connections, and main-current paths 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 their plastic cages while retaining the cages, boards, terminals, thermistors, and other reusable pack hardware.
• Desoldered the remaining cut lead sections from the boards and cleared the connection points with a solder sucker.
• Cut replacement main leads to length and bent them to match the required exit geometry.
• Spot-welded angled nickel interfaces onto the prepared main leads for attachment to the rebuilt cell arrays.

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 established a common charged starting condition for assembly; it was not a measured discharge-capacity result.

DeWalt Rebuild and Validation

• Reassembled the five-cell 5S1P battery array in the original carrier and orientation.
• Installed the positive-terminal insulators and tacked the new nickel interconnects in place.
• Added extra Kapton tape around exposed interfaces and contact areas for additional insulation.
• Partially installed the shell and performed an initial functional test in a small shop vacuum.
• Connected a third-party DeWalt adapter with USB output to a USB meter and selectable high-load resistor board.
• Held the electrical load until the resistor bank approached its thermal limit, then checked the resistor bank and pack temperatures.
• The meter showed approximately 4.80 V at 3.16 A, about 15.18 W.
• The resistor bank measured approximately 486.7 F, the pack measured approximately 91.9 F, and ambient temperature was roughly 80 F.
• Placed the partially assembled pack on the OEM charger, observed normal operation with no smoke or visible abnormal behavior, and allowed it to reach full charge.
• Trimmed limited plastic from the shell with side snips to clear the wider replacement nickel and completed final assembly.

The DeWalt pack passed the initial tool, resistive-load, thermal, charger, and full-charge checks. These are practical functional checks rather than calibrated capacity, cycle-life, or maximum-discharge qualification.

Assembly Assumptions

• Install a positive-terminal insulator on each new cell before laying out nickel.
• Preserve and reuse OEM carriers and insulation where intact.
• Use additional Kapton where replacement geometry creates exposed or compressed contact risks.
• Use 8 mm x 0.15 mm pure nickel for straight interconnects and local connections.
• Use 0.15 mm x 27 mm pure nickel H-strip stock to reproduce the wider OEM-style Ryobi cross-row bus geometry rather than stacking multiple narrow strips.
• 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.

Ryobi PBP005 Rebuild

• Preserved the documented OEM 5S2P layout and retained the original board, thermistor, terminal assembly, carrier, and usable insulation.
• Originally planned to reproduce the interconnects with 8 mm x 0.15 mm pure nickel, using parallel paths where needed.
• After reviewing the OEM stamped cross-row bus geometry, determined that stacking multiple narrow strips would produce an unnecessarily complex interconnect.
• Ordered and received 0.15 mm x 27 mm pure nickel 2P H-strip, Amazon ASIN B07VMGTVL5, to reproduce the wider two-row geometry more cleanly.
• Used the original stamped interconnect layout as the physical reference for the replacement cross-row bus geometry.
• Installed positive-terminal insulators and arranged the charged replacement cells in the original 5S2P orientation.
• Tack-welded the H-strip and remaining nickel interconnects to form the five parallel groups and required series connections.
• Reconnected the prepared board leads and associated sense connections to the corresponding battery connection points.
• Reinstalled the rebuilt array into the original plastic carrier and mechanically reassembled the pack.
• Retained the pre-energization checks for orientation, group-voltage progression, total voltage, insulation clearance, weld integrity, and thermistor placement before charger insertion.

Ryobi BMS Reset and Charger Validation

• The rebuilt pack was not initially accepted for normal charging after reassembly.
• Performed the documented J1 reset sequence on the retained Ryobi board.
• The reset succeeded and produced the expected two-LED indication.
• On the first OEM charger insertion after reset, the charger initially blinked red.
• The charger then transitioned to green, indicating that the pack was being accepted rather than remaining in the initial fault state.
• The pack is being left on the OEM charger for observation before further load testing.

Ryobi Validation Criteria

• The rebuilt 5S2P array is accepted by the OEM charger.
• All five parallel groups remain closely matched through initial validation.
• The pack returns to normal tool operation without abnormal heating or early cutoff.

Next Step

1. Continue observing the OEM charger session for normal behavior and any abnormal heating.
2. Confirm final charger status and termination behavior.
3. Perform an initial moderate tool-load test.
4. Recheck parallel-group voltages after the initial load to look for early imbalance.
5. Record charger, tool-load, and thermal observations before considering the Ryobi rebuild complete.

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.

Open Items

• Record the original Ryobi cell markings.
• Record the Ryobi parallel-group and total pack voltages from the rebuild if the pre-reconnection measurements were retained.
• Record exact spot-welder markings and successful settings for 0.15 mm pure nickel.
• Record final Ryobi charger termination, tool behavior, and thermal observations.
• Track the rebuilt DeWalt pack through normal tool use for any early imbalance, heating, or mechanical issues.

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