The Niterider MOAB (Mother Of All Batteries) Li-Ion battery driving the HID lamp allows for 11 hours at low intensity, 9.5 hours at medium, 7 hours at full brightness. Having an EXTRA MOAB BATTERY means that you can burn full intensity for 14 hours without needing to recharge anything.
The lamp also has a low-intensity LED option, which is more than adequate for doing low-speed dirt road climbing and adequate for some commuting. A single fully-charged MOAB battery will drive that setting for 480 hours.
This setup works perfectly. Has never failed or run less then the expected time. Batteries have been kept charged up, even during periods when I wasn't night riding. Both batteries have been used extensively this summer. Both are in great working order, driving the lamp as long as they ever have.
The connector style is I think the best, most robust one that Niterider has ever used. See the 2nd photo for close-ups of the connector.
$400 $350 shipped to anywhere in the lower 48, or make me an offer! Not doing business outside of the lower 48 USA.