rechargeables vs alkalines... difference in brightness

I have a friend who refuses to use rechargeable AAs in his LED flashlight. He says the reduced volts coming out of a rechargeable will make his beam significantly dimmer vs using alkaline batteries.

Is his assertion correct?

Thanks in advance.

Nick

The short answer is an Alk will start out around 1.5 volts and gradually in a steady type of curve drop to around 1 volt (when it's about considered dead). Where as a NiMH cell will steadily stay around 1.25 volts and when it is dead will quickly drop to around 1 volt. A form of sudo regulation really. On a light without regulation you'll get a steady light through the life of the batteries. On an Alk you'll probably be brighter for part of the life of the cell but as it curves below 1.25 volts you'll be dimmer for the rest of the life of the cells. Odd's are the NiMH will last longer in the light as well.

An upside is that the NiMH can take a significant current draw for those meaty high lumen lights.

So in essence on some lights (unregulated) your pal is partially right. Personally I'll take the NiMH any day, they last significantly longer in my lights and I get a nice steady brightness in my lights that are unregulated.

Welcome to CPF!

Show him one of those runtime graphs where alkies and NiMH's are compared. The "voltage sag" of alkies only keep the newer lights brighter for a short time. In the long run NiMH's win.

I *think* he might be stuck thinking about higher voltage making an incandescent bulb brighter (which is true for direct drive lights), but that's not the case with LED lights (which for the most part use electronic circuits), which are at their best (IMO, at least) when constant current is applied to them.

A lot of the led lights on the market are still running with three or more batteries and use direct drive or direct drive with a resistor. In that case the alkaline driven light will be brighter at startup, but will drop off fairly quickly. Using rechargeable batteries the light will may start off dimmer but will maintain a decent light output over time.

Bill

In Fenix L1D-CE Comparison Review -
Part 3 - "Practical" Stairway beamshots Post #96
I did "practical" stairway shots of the L1D-CE using alkaline and also NiMH - both in Turbo/Max - the NiMH looked brighter than the alkaline. (Note: the NiMH was an old and well used, humble 1600mAh RayOVac rechargeable.)

Fenix L1D-CE on Turbo/brightest setting for all shots -
Alkaline .................................................. ........ NiMH


I think this may be due to the fact the NiMH is capable of delivering higher currents than an alkaline.

Also there was a question of whether NiMH or Lithium primaries (eg: Energizer e2 AA) were brighter in the Fenix L2D-CE Comparison Review

I did a side-by-side comparison of some humble well used 1600mAh RayOVac NiMH vs. good Energizer e2 primary lithium AAs in

Part 2 - Fenix L2D-CE NiMH vs. Primary Lithium AA - Post #17

Note: the initial open-circuit voltage of lithium AAs like the Energizer e2 is about 1.7V which is normally quite a bit higher than the initial o-c voltage of an alkaline AA battery.

Also lithium batteries hold on to their voltage level almost until depleted. So from my comparison even though the NiMH were quite a bit lower voltage than the lithium - they performed about the same brightness level in the Fenix L2D-CE which is LED and current regulated.

The equivalent stairway shots for the L2D-CE using NiMH, alkaline and primary lithiums next to each other in -
Part 3 - practical indoors Stairway beamshots - Post #21
This one's harder to call but the NiMH is at least as bright as the lithium or alkaline.

Thanks a lot for the detailed replies. This exceeds what I was expecting!

i hate to admit it . . . .


But i myself felt the same way, until i began looking closely
at some of the flashlight discharge curves (run-time graphs).


Study a few of 'em, and it becomes very clear that Alkalines are a poor substitute
for a good set of rechargeable NiMH cells. Especially at brighter outputs.


In fact, now i've even purchased one of those fantastic
MAHA C-9000 battery charger/analyzer units.



I now realize the error of my ways.



Not to mention, it's better for the environment.

And it'll actually SAVE you money, in the long run.

(but, of course, we'll only blow it on more flashlights !)



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