I asked Hank what driver he used for D4Sv2 with Osram W2 and Luminus SST20-DR 660nm. He said the driver was FET+1+3. I was hoping it would be a 9A (+ FET for W2) constant current driver like in the K9.3. IMHO, running four SST20-DR with direct drive could be too much current. These are specified up to 3A per LED, so four of them in parallel would max out at 12A total current already. Using a Golisi S43 or PLB55-A (Keeppower 5.500mAh) battery could deliver way more than 12A. With 9A constant current without FET each LED could be driven safely at 2.25A per LED.