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-   -   confused about mAh (https://forums.steves-digicams.com/batteries-power-packs/10827-confused-about-mah.html)

surfnron Jun 21, 2003 10:01 AM

confused about mAh
 
It's been years since I used rechargeable batteries. I Stopped because they just didn't last very long. From what I read on these forums, they are much better now.

If I have a radio that uses AAA batteries, will I get longer use from alkaline or rechargeables. The alkaline ratings go from 200 mAh to over 1100 mAh. The rechargeables I found were 800 mAh.

Is it JUST a matter of cost for using rechargeables?

Thanx,

Ron

sjms Jun 21, 2003 10:24 AM

the mah (milli ampere hour) is the power density. as far as the cost yes it would be considerably more cost effective to use nimh batteries. in AAA sizes 800mah is currently the top.

nimh batts don't have the memory problems of the nicad batteries.

nimh do quite well in the high draw catagory units like digicams.

on the down side after charging they tend to loose about 20% of their charge in the first 24hrs then after that its incremental. you can keep them on a charger for up to a year without damage. i usually have 3 sets of 4 on charge at any given time.

voxmagna Jun 21, 2003 11:33 AM

In days not so distant past, Alkalines would outstrip re-chargeables on their ability to deliver high current for short periods (Note this is different to mAh rating). So taking an Alkaline and a NiCad or NiMh battery, the Alkaline would win on max juice supply for short periods.

Things have moved on. Now NiMH is better than Alkaline and NiCad on capacity for size and peak current. However, most advances have been in the popular AA size. I'm not so sure about the less popular AAA's.

As sjms says, self discharge is the drawback of re-chargeables. Whereas Alkaline and Lithium are fine in clocks radios and calculators that get intermittent use. If you don't mind re-charging your AAA's every few months, they might suit you. BUT you can buy 2 sets, 1 with charger, and keep that set plugged in all the time. Make sure the charger is designed to take AAA cells and choose a 4-6 hour one rather than a fast charger.

surfnron Jun 21, 2003 1:33 PM

Thanx, great answers. I'm still not clear though. Will batteries rated at 1100 mAh last longer than ones rated at 800mAh in something like a walkman radio? It seems that way to me, but every part of this digital "thing" has such a steep learning curve...

Ron :shock:

sjms Jun 21, 2003 1:43 PM

yes but as you stated alkaline batteries at 1100mah. they are only good for 1 use and then chuck them in a land fill. 800mah at 500+ recharges last a lot longer.

HaveBlue Jul 10, 2003 10:16 AM

A lot of people confuse battery capacity and battery draw. A higher capacity battery has more power available to use for a given amount of time.

A car battery is a good example. A 1000-amp hour car battery would run a long time without being recharged. But when you start to increase the power draw (measured in amps) by turning on the headlights, brake lights, cigarette lighter, fan and radio the battery life is shortened.

A smaller 500-amp car battery would not last as long under high-power draw situations but could last just as long if the power draw were less by cutting off the car accessories.

Some digital cameras have lots of accessories and some have just a few. Large mechanical zooms, LCD screens, continuous auto focusing and processing of large picture file drain lots of power out of small batteries. “Lighter” digital cameras with no LCD display, no zooms and small picture files will operate very well with less powerful batteries.

Manufacturers are trying to squeeze more power out of small batteries by packing denser and better quality material. You can get longer power times in the digital cameras if your camera needs it. More power hungry digital cameras NEED the more powerful batteries.

sjms Jul 10, 2003 10:58 AM

that is correct. under the equivelent draw a 1000 should last longer than a 800. but if the 800 is rechargable 500 times and the 1000 is a throw away think about it.

surfnron Jul 10, 2003 8:03 PM

It's much clearer now. Thanx for all the replys. Short term it seems to be easier to use alkaline. Long term, it's cheaper to use rechargeables, even when you factor in the cost of the recharger.

Ron

Laserjock Jul 10, 2003 10:55 PM

The mAh rating of a battery is the batteries ability to deliver a constant current at a fixed voltage for one hour.

For example an 1100 mAh 1.2V AA battery can theoretically deliver 1100 mA (1.1A) of current for 1 hour at 1.2V. An 800mAh should give 800mA of current for one hour.

NiMh batteries do well in digital cameras because of their ability to deliver their current while maintaining their voltage.

Alkaline batteries do not do well in high current draw devices such as digital cameras and typically die very quickly. Hope this makes it more clear.

-Laserjock-

voxmagna Jul 11, 2003 5:42 PM

Following the previous posting and analagy to car batteries, the main reason for upping the ampere hours, is not just more power to run the lights etc. When you think about it, most of the time, this load is met by the generator.

It's all to do with 'Cranking Current'. Generally the higher the ampere hour capacity of a lead acid battery, the higher the cranking current. So a V8 or diesel car will have much the same electric power load. But try starting your V8 or diesel in sub zero temperatures (cold thick oil) and you need BIG cranking current. However battery makers have got clever. They now use the same plate area, but get them closer together. The battery continuous capacity and size is about the same - but it can deliver more cranking current. The problem is, to much continuous cranking can burnout the battery sooner.

So it's just the same with digicams. Their equivalent of cranking current is the high peak currents drawn by the digital circuitry. It might seem as though your load is 600 milli amps continuous, but that's just the average your meter is showing. Digital is about pulse load current - and pulses aren't direct current! So as the power density goes up (equivalent of closer plate spacing) - watch the self discharge rate when stored, which will increase over the same period. Or think about first turning on a digicam, the processor will be very active, the zoom lens motors will be running etc - that's going to mean more than an average power drain of 600mA.


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