DIY clone of Sennheiser's overpriced BA2015 battery pack reveals a $0.02 trick

A hardware tinkerer reverse-engineered Sennheiser’s BA2015 battery pack, used across much of the company’s wireless microphone lineup, and found the proprietary unit is essentially two standard NiMH AA cells in a plastic shell with a cheap NTC temperature sensor as the only added component. The third contact on the pack signals to the microphone that rechargeable cells are present, preventing the dock from attempting to charge alkaline batteries — the sole genuine function justifying the markup. Most of the smart-battery features Sennheiser advertises actually live in the microphone itself, not the pack.

The author tore down an original, modeled a replacement case in OpenSCAD, and built a working clone using two flat-top Panasonic cells, a small magnet for the button contact, a paperclip as an internal conductor, and a 10kΩ NTC with a beta around 3200. Printing the case on its side avoided weak layer lines along the thin retention tabs. The total parts cost is a few dollars per pack versus Sennheiser’s pricing, which third-party manufacturers already undercut dramatically.

The verdict is pragmatic rather than triumphant: the homemade pack works but is fiddlier and less robust than off-the-shelf third-party replacements, so the exercise is more a protest against vendor lock-in pricing than a practical recommendation. The OpenSCAD source is published for anyone who wants to replicate it.