Electronics, Lighting, & Gadgets - Amp hours and Alkaline batteries

How many amps are C-cell alkaline batteries?

Duracell does not say specifically, but I read something like 8000 mAh.

I'm trying to figure out how much life my Lowes Task Force flashlight has with it's two c-cell batteries if I use alkaline disposables.

Are they 8000 mAh?

If so, that's like 8 amps? Right?

My light is 3 watts.

Alkaline batteries are 1.5v.

1.5 x 2 = 3 volts.

3v x 8 amps = 24 hours at 1 watt. Right?

So my 3 watt light should burn for 8 hours on two C-cell batteries.

Am I missing anything?

Here ya go: http://www.flashlightreviews.com/reviews/taskforce_3w2c.htm (2.5 hours to 50% output).

I'd suggest using NiMH cells, they'll be able to maintain high current for longer and you won't have to keep buying them over & over. Batteryjunction.com carries them.

mAh isn't just the number of amps, it tells you how many amps for how long. In an ideal world 8000 mAh means the batteries can provide 8000 mA for 1 hour, or 1 mA for 8000 hours, or anything in between. The rating only applies at very low currents, maybe 100th of the rating, ie 80 mA. If the light is operating at 3 W its pulling 1 amp out of the batteries which significantly reduces their effective capacity. That's why the actual runtime is so much lower than your correct "ideal" calculation. Not sure if 8000 mAh is right for C but I know AA is around 3000 and D around 16000, so it seems reasonable.

I'd suggest using NiMH cells, they'll be able to maintain high current for longer

Why is this?

Why is this?

I believe the scientific reason is that they have low internal resistance.

it's just the chemistry of the battery.

I invested $50 in some NIMH C's and a charger. They don't work in the light after being charged for 16 hours per the instructions.

What could be wrong?

Maybe they're faulty. If you have a multimeter, check their voltage.

Actually, I just needed to stick a penny between the +terminal of the battery and the head. It worked fine.

The package on the Energizer batteries said 2400 mAh. Is that right? Their website says AA, C, and D batteries all have the same amp hours. How could that be?

Actually, I just needed to stick a penny between the +terminal of the battery and the head. It worked fine.

The package on the Energizer batteries said 2400 mAh. Is that right? Their website says AA, C, and D batteries all have the same amp hours. How could that be?

Energizer is ripping you off, by selling you a AA in a C-sized or D-sized shell for way more money.

If you want a proper NiMH C cell, here's a 6000mAh model from Batteryjunction: http://www.batteryjunction.com/tpeh-t6000.html And here's a smart charger to go with them: http://www.batteryjunction.com/tpec-ttg3000.html

Energizer is ripping you off, by selling you a AA in a C-sized or D-sized shell for way more money.

That's real mean of them. So mean that I took back the batteries and charger to the hardware store. I told them the batteries and charger did not suit my needs.

Then I found out that they make adapters to put AA batteries in stuff made for C-cells. That changes everything. I have a couple of AA chargers and batteries (2100 mAh)

All I need is a little more than an hour of good light. Would that do for now?

That's real mean of them. So mean that I took back the batteries and charger to the hardware store. I told them the batteries and charger did not suit my needs.

Then I found out that they make adapters to put AA batteries in stuff made for C-cells. That changes everything. I have a couple of AA chargers and batteries (2100 mAh)

All I need is a little more than an hour of good light. Would that do for now?

I did another Google search. One person at CandlePowerForums reported that his Task Force light runs over 4 hours using 5000mAh C cells.

So we go 4 x 2100/5000 = 1.68 hours, and then multiply that by a 0.7 Reality Correction Factor to account for unknowns like the condition of your AAs, and we get about 1.2 hours to 50% brightness. Beyond that, it will just run dimmer. So I think you got a plan there :)

So I actually made a C to AA adapter out of some foam construction material. Now my 2100mAh AA's are in my light ready for action along with two fully charged AA's.

So when the AA goes dim, it goes fast? I figure I'll carry some Alkaline C's as backup.

My commute is 45-55 minutes. I'm a teacher so I'm seldom riding to and from work in total darkness. Even if I leave really early, I only need light for the first half hour unless it's the end or beginning of DST. And in the dead of winter, I need to stay pretty late to be riding in the dark the whole way home.

With the money I saved by returning the C nimh batts and charger, I can afford another Task Force light (presently on sale for $24.95) or maybe a Fenix light. Then I might ask Santa for some good nimh c's and a good smart charger.

So when the AA goes dim, it goes fast? I figure I'll carry some Alkaline C's as backup.

From the graphs, I got the impression that it will drift down gradually, for the most part. You might not ever notice, if your commutes are typically under an hour.