We’ve cleared the waiting list and have already sent off a few extra headlights since Christmas. So now it’s time to get back to more interesting blog posts.
One of the most common questions I get asked is:
‘How long does the battery last?‘
It’s a good question to ask. The joy of using a high-powered headlight would be somewhat reduced if you needed to carry 20kg of spare batteries. Fortunately, a single set of 18650 cells will last most people an entire night.
If you missed my introduction to 18650 cells, then you can read up on them here.
The minimum runtimes you’ll get with two Xtar (Panasonic) 3100mAh cells are:
- 3 hours on the spot,
- 4 hours on the flood at 100%,
- 10 hours on the flood at 40%,
- 28 hours on the flood at 15%,
- 85 hours on the flood at 5%,
- 400 hours on the flood at 1%.
For me personally, this means that by using the 15% flood most of the time, and only turning the spot when I need to find something, I can go all night on a pair of 18650 cells (which only weigh 45 grams each). It sounds like I am sacrificing light to make it last all night, but I’m not. The 15% flood is still brighter than most other headlights at full-power!
Below are some plots of the change in light intensity produced by the V3 over time. Each line represents a different power level.
Unfortunately, since the runtimes vary between 3 and 400 hours, it’s hard to show them all on the same graph. So the first graph has a logarithmic time scale. This lets us see all the data on the same graph.
We just need to remember that the markings on the far left represent 6 minutes each, while the markings on the far right represent 100 hours each. Only the 1% level (which lasts 400 hours) gets into the 100-hour markings.
Unfortunately, not everyone thinks in logarithmic scales, so I’ve removed the lowest mode so that you can visualise it on a linear scale:
Comparing the levels
The important thing to remember with these graphs, is that the flood and spot beams are very different, so they were measured in different ways. There are no numbers on the vertical axis so that nobody gets confused. You cannot compare the intensity of the flood and the spot on these graphs. The graphs make it look like the spot is dimmer than the 100% flood, but this is not true.
The curve at the end of each line shows how the light gradually dims when the battery is almost flat. These lights are ‘semi-regulated’. This means that they have a smart circuit inside them which maintains a constant level of light (see the flat bits in the graphs) until the battery is almost dead, then the light level drops gradually. This is better than ‘unregulated’ which starts to dim as soon as you turn it on. It’s also better than ‘fully-regulated’ which stays bright for a few minutes longer but then goes out completely without any warning.
So how long does the spot really last?
Earlier I mentioned that the spot only lasts 3 hours, but the graph show us that it continues to shine up to about 8 hours. 3 hours is how long it lasts in regulation before it starts to dim slowly. So the way to think of it, is that it’s a great beam for 3 hours, a good beam until 6 hours, and then a dim beam until 8 hours.
So how long does the battery last?
Long enough for most of us!