Milwaukee M18 Battery Reverse Engineering

Original Article ↗ Hacker News Discussion ↗

Battery electronics & reverse engineering

  • Commenters appreciate the detailed teardown, noting the use of a low‑power MCU plus an analog front-end (AFE) ASIC.
  • The AFE handles per‑cell voltage measurement, current sensing, fault protection (MOSFET cutoff), and cell balancing control, while the MCU manages higher‑level logic and communications with tools/chargers.
  • The MSP430’s deep sleep is highlighted as key to not draining packs in storage.

Charging, BMS, and cell balancing

  • Clarification that the Milwaukee pack circuitry is not the charger; the real charging regulation lives in the external charger.
  • In the pack: SOC indication, protection, current negotiation with tools, and (theoretically) balancing—though several note Milwaukee appears not to implement balancing in some lines.
  • M12 and certain DeWalt packs are reported to lack active balancing despite having sense pins, leading some users to manually balance via hobby chargers or external plugs. Experiences vary between “no problem in 10 years” and “all went out of balance in 2 years.”

Compatibility, standards, and adapters

  • Debate about (rumored) EU moves toward standardized tool batteries; some link to actual EU battery regulation but it’s unclear whether it mandates interchangeable power‑tool packs.
  • Some see standardization as environmentally and economically beneficial; others call it unnecessary regulation since cross‑brand adapters and third‑party packs already exist.
  • Adapters are common but can bypass low‑voltage cutoff depending on where protection is implemented (tool vs battery), risking over‑discharge.

Cost, ecosystems, and sales tactics

  • Many note tool batteries are disproportionately expensive compared to raw cell prices, likening them to ink cartridges.
  • Strategy: buy tools bundled with batteries (often on sale) rather than standalone packs; Home Depot “hackable” promos and deal‑watching communities are frequently cited.
  • Tool platforms intentionally lock users into ecosystems; some expect only regulation would produce true cross‑brand compatibility.

User experiences & performance

  • Milwaukee M18/M12 systems receive strong praise for durability, pack longevity, charger behavior (round‑robin, safe standby), and breadth of tools.
  • Some prefer DeWalt for woodworking and Milwaukee for high‑torque and automotive work; Makita and Ryobi are seen as good value, especially for DIY use.
  • New “tabless” and high‑capacity cells are reported to significantly improve power delivery.

Safety, failures, DIY and knockoffs

  • Stories cover NiCd pack disappointment vs long‑lived modern Li‑ion, DIY pack rebuilds with added BMS, and one office fire from drone battery charging.
  • Opinions differ on knockoff batteries: experiences range from fine and higher‑capacity to poor cold‑weather performance and under‑spec cells; fakes of OEM packs are also reported.
  • Some run tools from bench power supplies via gutted battery shells; others explore but question USB‑C, noting the very high power levels these tools can draw.