Question on run time for battery upgrade

The Lenser M7R comes with a 2200mAH 18650. My question is if I replace this with a 3400mAH, will I see a linear increase in runtime, or does it work like that?

ie: This would represent a battery capacity increase of 1.55. So hypothetically, if the runtime on high is 2h, could I expect it to increase to 3.1h?

TLDR: kinda; compare cells at this link http://lygte-info.dk/info/batteryIndex.html

I seem to understand watt-hours (Wh), mWh, etc. (power) better than Amps (current), so I usually think in those. Cell runtime is directly proportional to how many Wh the light can get out of a cell. (V=IR, so it is also proportional to how many Ah it can get, but I always prefer W for some reason--I think because I think of LED as lumens-per-W.) The number of Wh a cell can give depends on the cell design--some are designed for more capacity at higher currents, some for long runs at lower currents. Anymore, I never buy a cell without consulting the work of HJK at the link above.

Depending on the use, I'll sort the table differently, and then compare mWh. Some of my cells are for lower current, long-run applications, so I'll look at the mWh of .2A or 3A, down to a cutoff voltage of 3.0 or 2.8. Some of my other lights are higher current, so I'll look at the mWh capacity at 10A or higher, down to 3.4 or 3.6V. In a constant-current light, runtime should be roughly proportional to the mWh at your given current and cutoff voltage.

One big caveat--the driver of the light will play tricks with your runtime. If the light doesn't have a constant-current driver (just a resistor, or relatively "dumb" electronics), my statements above aren't exactly true. Even relatively "smart" lights, at the end of cell life, will just step down current draw and dim down the LED to get the last bit of juice out of the cell. So, depending on how you measure runtime, there might be some funny results as different lights and drivers interact with different cells. The ANSI runtime figure (that's what manufacturers usually quote) is silly to me--the clock is still running down to 10% brightness, which is usually useless for whatever application required 100% brightness. There also can be funny runtime results when putting high performance cells in "smart" lights--a really good cell might allow a light to draw a lot more current at turn-on, and actually have a shorter runtime than a lower-capacity, higher-resistance cell that doesn't allow as much current draw.

Sorry, wordy answer to a question that is simple to ask, but can be tricky to answer completely!

OK. Thank you. The P7R does not have constant current electronics. The 2200mAh battery is 8.14Wh and the 3400mAh is 12.58Wh. Does that assist with making an estimated extension of runtime with the larger battery?

I don't trust manufacturer ratings, I trust HJK. Depending on what cells they actually use, and what current you're using them at, the improvement could be as little as 34%, and as much as 65%. The improvement will be more if you're going from an old 2200 to a new 3400. You'll see on the HJK table that the cells rated at "2200 mAh" give these mWh capacity results down to 2.8V:

And, cells rated at "3400 mAh" give these mWh results:

That's actually relatively interesting to me. It looks like a lot tighter grouping of "3400mAh" cells, indicating that HJK has tested quite a bit of garbage that is rated at "2200mAh" but a lot less at "3400".

Anyway, I wouldn't personally buy a cell if I I couldn't identify the original manufacturer and look up independent test data (for example, a "LEDLenser" 18650 was originally manufactured by someone, but I couldn't figure out who with a quick search--someone knows, but they don't want to make it easy to figure it out and do a price comparison of the LEDLenser re-wrap vs an OEM).

I'd go with the 1.55 runtime! I think of the mAh size at how big the fuel tank is!! LOL

Tony Rama said:

will I see a linear increase in runtime

Click to expand...

yes, larger capacity, longer runtime

and the battery will weigh a bit more
and might be longer too.