Why choose a battery with a lower mAh rating?

[ssssnake529]

When choosing rechargable batteries, are more mAh always better?

I'm looking at getting some spare batteries for my Fenix headlamp. (21700 size.)

On the Fenix site, there are two batteries, both 21700. One is 4000 mAh. The other is 5000 mAh.

The 4000 mAh version is a few dollars more expensive than the 5000 mAh version.

Why would I buy the one with 4000? There's nothing about it that indicates that it is special. It's not designed for cold temps.

What am I missing?

Fenix ARB-L21-4000P Rechargeable Battery - Fenix Lighting

ARB-L21-4000P is a high-capacity 21700 Li-ion rechargeable battery built for more power and longer runtimes. Battery capacity 4000mAh. 500 charging cycles.

www.fenixlighting.com

Fenix ARB-L21-5000 Rechargeable Battery - Fenix Lighting

ARB-L21-5000 is a high-capacity 21700 Li-ion rechargeable battery built for more power and longer runtimes. Battery capacity 5000mAh. 500 charging cycles.

www.fenixlighting.com

 

[hamhanded]

In general, lower mAh ratings for a given chemistry can indicate a higher current capability/lower internal resistance, lower self-discharge rate, higher rated cycle count, some combination of the three… or sometimes just that the cell is cheaper (and the manufacturer is honest about the reduced capacity that comes with that).

 

[pc_light]

+1 what @arrgh said.

What am I missing?

See the specifications for the batteries' power output capabilities in the references you indicated. The -4000P is capable of Maximum Output of 18A burst and 10A continuous. Whereas the -5000P as 7.5A max current.

For example, for high output lights designed to be driven at the higher/highest current draw the lower max current battery might not be capable of delivering the maximum output.

 

[ssssnake529]

I missed that issue of power output.

That makes sense.

So, the 5000 version will provide steady power for longer, but the 4000 may burn brighter on the highest settings.
(assuming that the flashlight needs more than 7.5A current to take full advantage of its brightest light setting.)

I appreciate the help.

 

[alpg88]

it is not always the case, larger capacity does not always mean better power handling, (mostly true for identical chemistry batteries) but in general it is quite the opposite actually, higher power batteries use different chemistry which allows for higher current, but lower capacity
Fenix does not make batteries, they rewrap quality brands, so you really want to find out what cell is inside, 4000mah may be a different chemistry vs 5000mah. but your light is not a power hungry light. you should be able to see longer runtimes from 5000mah,

 

[Havok]

I'm not sure what's under the 4000mah wrapper, but under the wrapper of my 5000mah was an LG M50T.

 

[Jay R]

There are 3 working parts to a battery or cell. The electrolyte which holds the charge (power) and the anode and cathode that take the charge out of the electrolyte. If you make the anode and cathode bigger, you can take more charge out in one go but you have less room for the electrolyte so you can't hold as much charge. If you make the anode and cathode smaller, you have more room for the electrolyte but you can't take as much power out in one go.
Of course, different quality and different materials also play a factor but for the same chemistry in the same size battery, the above rule applies.