Run time calculation help needed

I just picked up the Terralux 1000 lumen drop in for a 4 - 6 cell maglite. Terralux quotes the run times as 2/6/37 hours on High/Med/Low. I assume they're quoting times on a 6 cell set up rather than 4. I am using 2 adapters that allow you to run 3xAA in a D size format so I can use this is a 2 x D cell Maglite. So what I'm wondering is if this thing runs for 2 hours on 6 D cells, how long will it run on 6 AA cells ? Either NiMH, Alkaline or LIthium. ( I happen to be using the second tier Lithium cells ( not the best ones, but hopefully better than Alkaline )


Thanks !!

With Alkalines, it depends a lot on the draw. The larger draw, the less capacity. Energizer has some charts on their website you can look through, but basically with D cells if you run that at 25mA, you'll get crazy capacities around 20500mAh according to Energizer. I'm guessing it will be pulling higher currents than this though. The ultimate lithium batteries have a capacity of around 3000mAh, and keep that capacity even at higher drain rates.

If you have a current meter, you could measure the current at the tailcap with the lithiums, and calculate the runtime from that. Basically, since the batteries are in series, you still only get 3000mAh of capacity (just at a higher voltage). If you read 1A of current draw, you would calculate 3000mAh/1000mA = 3h.

Hope this helps!