NiMH AAs with C/D adapter vs alkaline C/D cells in high drain devices

Just wondering how NiMH AAs using an adapter to use them in place of a C or D cell would compare in runtime to using Alkaline C or D cells, specifically in a high drain application like a flashlight.

The specific flashlight I have in mind is the 3W Taskforce with the Luxeon LED. I know that using 2 fresh C alkalines, the light is pretty thoroughly dimmed after a couple of hours. I know a lot of that is also due to the fact that the approx 1 amp current demand kills the alkalines, but by how much? A typical C is rated at, what, 8000 mAh or so and about 20000 for a D cell, right? So what kind of capacity could I reasonably expect from each of these at, say, a 1 to 1.5 amp drain?

• AA NiMH rated at 2,500 mAh
• AA Eneloop NiMH rated at 2,000 mAh (I believe someone told me they are happier with high loads than standard NiMH cells?)
• C Alkaline rated at 8,000 mAh
• D Alkaline rated at 20,000 mAh

On a related topic, can someone please explain the whole "C" thing when talking about currents? Like if you're talking about a 3C current discharge rate, what does that mean?

Hello Avastar28,

You can compare the results in the NiMh and Alkaline shoot out threads which can be found here.

Tom

From what I understand, a 1C discharge is discharging the battery at it's rated capacity.

So a 1C discharge rate for a 2000 mAh NiMh Eneloop would be 2000 mA.

I think you would get shorter but a better regualted runtime with 2 NiMh AAs instead of 2 C cells.

I use Eneloops in my 2C Mag with a Mag 2Cell LED. The spacers are great and the light seems strong and bright till the end when it drops off kinda fast. I will probably not buy anymore alkys.

The total runtime is longer on the alkys but at some point it is dimmer too.

At 1 amp load you will probably get less that 3 watt hours from an alkaline C cell. A high capacity AA NiMH can deliver about 3 watt hours... You may find that AA NiMH battery power the light for slightly longer than the alkalines if it is well regulated. Alkalines really start to suffer when their load exceeds 100mA, and at 1 amp they perform very poorly.

Thanks for the link to the shootout. They didn't have any C cells but as much as the D's dropped then I think you're probably correct that the C's would have less capacity than the AAs (sad reallly). As for the "Heavy Duty" I think it's safe to say they were anything but. 6 seconds to flat for the AAA's at a 1 amp load. Amazing.

smarter just to run C size NIMH, 5000+ mAH capacity and 1A+ drain is no problem.