Battery Case & Housing Repair Kit for Milwaukee® M18 18V HD 12.0Ah
DIY rebuild housing + charging/protection PCB + nickel strip for 15 × 21700 HIGH DEMAND packs. Cells are NOT included.
The HD 12.0 is the most expensive pack in the M18 range — and a dead one is rarely dead all the way through. Fifteen 21700 cells sit in five parallel groups; when one group drops out, the charger refuses the whole pack and the other fourteen cells go in the bin with it. A fresh housing, a new protection board and a matched set of cells brings it back — and because you pick the cells, you control whether the rebuilt pack matches the original or beats it.
What You Get
- 1 × Upper + lower plastic housing (impact-resistant ABS/PC, black)
- 1 × Charging & protection circuit board (PCB) with fuel-gauge LEDs
- 1 × Nickel strip set — pre-cut, ready to weld
- 1 × Screw set
What You Need to Supply
- 15 × 21700 lithium-ion cells in 5S3P — high-drain 30A+ recommended (4.0Ah cells × 3 parallel = a 12.0Ah pack)
- A spot welder — do not solder directly to cells
- Basic hand tools and a multimeter
Nickel strip is included. A 15-cell 21700 rebuild needs heavy strip and plenty of it, and most kits at this price make you source it separately. Ours ships pre-cut for the 5S3P layout, so all you add are the cells.
⚠ 21700 cells — not 18650. A 21700 cell is 21mm across and 70mm long; an 18650 is 18mm across and 65mm long. They look almost identical in a photo but are not interchangeable, and 18650 cells will not fill this housing correctly. Counting cells is not enough to identify your pack — measure one cell from your old pack before you order.
Fits Milwaukee M18 HIGH OUTPUT part number: 48-11-1812 (HO HD12.0) — 15 × 21700 packs.
Is This the Right Kit for Your Pack?
This is the HD 15-cell 21700 housing — the largest in the M18 range. Check both the cell count and the cell size in your old pack before ordering.
| Your Pack | Cells Inside | This Kit? |
|---|
HD 12.0Ah
48-11-1812 | 15 × 21700 (5S3P) | Yes — this one |
HD 9.0Ah
48-11-1890 | 15 × 18650 — same count, smaller cell | No — see our HD 9.0 kit |
XC 6.0 / 8.0Ah
48-11-1865 / 48-11-1880 | 10 × 21700 (5S2P) | No — see our XC6/XC8 kit |
XC 3.0 / 4.0 / 5.0Ah
48-11-1828 / 48-11-1840 / 48-11-1850 | 10 × 18650 (5S2P) | No — see our 10-cell 18650 kit |
CP 1.5 / 2.0Ah
48-11-1815 / 48-11-1820 | 5 × 18650 (5S1P) | No — see our compact kit |
The easiest mistake to make: the HD 9.0 pack also holds fifteen cells, but they are 18650s in a different shell. If you counted fifteen cells, measure one before ordering — 21mm across means this kit, 18mm across means our HD 9.0 kit. Unsure? Message us a photo of your open pack and we will confirm the fit.
Specifications
| Nominal voltage | 18V (5 series) |
| Cell configuration | 15 × 21700, 5S3P |
| Target pack capacity | 12.0Ah (with 4.0Ah cells) |
| Housing material | Flame-retardant ABS/PC, black |
| Dimensions | 6.9 " L × 3.8" W × 4.6" H |
| Weight | 17 oz (kit only, no cells) |
| Brand / MPN | Janllenton / JYX-AA-005 |
| Warranty | 9 months on the case and PCB |
How It Goes Together
- Open the old pack and photograph the balance-lead wiring before removing anything.
- Build a 5S3P block from 15 matched 21700 cells, spot-welded with the supplied nickel strip. Weld the three-cell parallel groups first, then join the five groups in series.
- Connect B−, B1, B2, B3, B4 and B+ to the PCB in order — check each tap with a multimeter before powering up.
- Charge fully on a Milwaukee® M18 charger and confirm all four fuel-gauge LEDs light.
- Close the housing and fit the screws.
Safety — please read. This is a DIY project for people with hands-on electrical experience. A 15-cell 21700 pack stores more energy than anything else in the M18 range and can deliver very high fault currents. Lithium cells can vent, catch fire or explode if shorted, over-discharged, punctured, or mixed by age and capacity. Use cells of the same brand, capacity and state of charge, never solder directly to a cell body, and assemble in a clear, non-flammable work area. If you are not comfortable with any of this, please do not buy this kit.
Shipping & Returns
- Free USPS Ground Advantage shipping, dispatched from our US warehouse within 1–2 business days.
- 30-day returns accepted.
- Volume discounts apply automatically at checkout — save more on 2, 3 and 4+ kits.
- Rebuilding several packs? Message us before ordering for a multi-unit quote.
Compatibility notice: This is an aftermarket replacement part manufactured and sold by Janllenton. It is not manufactured by, sold by, affiliated with or endorsed by Techtronic Industries or Milwaukee Tool. "Milwaukee®", "M18®" and "REDLITHIUM®" are registered trademarks of their respective owners and are used here solely to describe which tool batteries this part fits.
⚠ California Proposition 65 Warning: This product can expose you to chemicals including lead, which is known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to P65Warnings.ca.gov.
Milwaukee®, M18™, DEWALT®, FLEXVOLT®, Makita®, Bosch® and all other brand names are trademarks of their respective owners. This is an aftermarket product made by Janllenton. It is not manufactured, sponsored or endorsed by any of these brands. Brand and model names are used only to describe compatibility.