A lithium starter battery in the DIN 019 footprint - 353 x 175 x 190 mm, SAE side terminals plus an M8 stud on each post, 15.7 kg pack against roughly 45kg for an AGM 150Ah equivalent. 1500 cold-cranking amps. 220A continuous, 300A pulse for three seconds - more headroom than any 12V diesel that lives in a DIN 019 case actually needs.

The BMS is sized to live behind an alternator. Recommended charge window 14.2-14.6V, squarely inside every regulated charging system. Over-voltage trip set at 15.0V pack / 3.75V per cell - deliberately high. Most lithium starter packs trip at 14.6V/3.65V, which causes false cut-offs during normal alternator operation and throws a charging-system fault on the dashboard. We tuned ours to ride those excursions without blinking. Automatic reconnect at 14.0V if the BMS does protect, and even then charge and discharge MOSFETs are independently switched - the battery stops accepting charge while still supplying the bus, so the alternator never sees a load-dump.

Pre-charge function on cranking limits inrush. Hibernation mode kicks in after ten minutes of no current draw under 3V per cell, dropping BMS consumption to 0.16 mA - leave it on a trickle over winter and it still wakes up in spring on charge, discharge, or the TITAN app reconnecting.

Twelve prismatic cells in a 4S3P module configuration inside an ABS case. Dual active and passive cell balancing carried over from the main range - active balancing moves energy between cells when the delta gets large, passive bleeds handle the smaller differences (both kick in at 3.4V cell voltage, active at a 30mV delta, passive between 15 and 30mV). Internal resistance under 10 milliohms. Discharge from -20°C, charge from 0°C, FET thermal protection at 90°C. Bluetooth monitoring through the TITAN app.