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For those wanting 26650s, check this out.

Dr_Evil

Dr_Evil

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I was in my local Batteries + and noticed these. The price was somewhere around $12.

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The package says 4600mAh. I figured it wouldn't hurt to buy one since I needed another one. The updated packaging says 13 amp max draw. I tested the capacity using a .5 amp draw. The capacity came out to 4343 and 4338 the 2 times I tested it. The remaining 26650 I bought from Light Hound a few years ago only came out around 3500.
 





More important for our larger diodes is how much voltage drops under load, a NUBM44 with a SXD driver takes 3 amps from 2 x 26650's in series.

The purple Efest rated 4200mAh and 40 amps continuous and 60 amps surge hold at 4.0 volts from a full charge floating at 4.17 volts when loaded with a big 1 ohm resistor, but the IMREN 5200mAh drop to 3.5 volts into the same 1 ohm load.

This matters as the SXD drops out at 6.7 volts.

Typically higher mAh has higher internal resistance as well, the IMR/INR formulations are better for high drain, but if you have plenty of room and can series parallel several pairs than the higher mAh may be better for say, a portable self contained laser show.
 
It's not really a 'typical' relationship, as batteries get better you can get both an increase in capacity and decrease in internal resistance for a give form factor.

Most lithium cells are designed for relative low loads (under 1C) for use in laptops and similar applications. There are specialty cells designed to have a low internal resistance at the cost of capacity though. A typical application for those would be cordless power tools, but also applications like drones and other things that are required to work at high powre but only a short duration of time.

If you want to build a laser pointer or flashlight with a runtime of well under an hour you could consider these high peak power cells, although your heatsinking will also have to cope.
 
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