New Delhi, July 7 -- A 'battery management system' is a small microcontroller inside a lithium-ion pack. It regulates charge and discharge, and in the cheap packs powering most of Delhi's e-rickshaws, it exposes its settings over Bluetooth as readable and writable.

One of these toggles the switch connecting the battery to the motor. The pack pairs by a method that a Bluetooth specification calls "Just Works," a connection with no authentication requirement that was chosen because the pack has no keypad for a code and it saves power. It was built to answer any device within a range of about 15 metres and never to ask who is asking.

So, when e-rickshaws across India's capital began stopping dead last week, and strangers demanded Rs.200 (o...