what doe mAh ratinge really mean

[pierhogunn]

Do mAh ratings on rechargable batteries mean that:

a 1.2 volt batter rated at 2500mAh will deliver 1.2 Volts at a maximum current draw of 2.5 amps for 1 hour?

[drumpriest]

yep, milli-amp-hours, from the wiki

http://en.wikipedia.org/wiki/Ampere-hour

[poolhound]

You got it.

mAh is basically the capacity of a battery in terms of how long it will run. If everything were perfect and there were no other losses (it isnt and there are ) then if your device were to use 50mA and you had a 1000mAh battery it would run for 20 hrs.

Most battery powered devices do not have a constant current draw and batteries do lose charge when not use and change characteristics at different temps so its not easily possible to calculate things emprically. For example if you have a digital camera and only ever just press the shutter, never reviewing pictures or using the flash the batteries will last way way longer as these two feature represent the highest power draw.

Its easiest to think that with all things in your device being equal a battery with a rating of 2000mAh will last twice as long as one rated at 1000mAh.

[poolhound]

yep, milli-amp-hours, from the wiki

http://en.wikipedia.org/wiki/Ampere-hour

If you follow the link "electrical batteries" on this page to http://en.wikipedia.org/wiki/Battery_(electricity) and look at "capacity & discharging" and "battery lifetime" you will find out more than you ever probably wanted to know about how batteries discharge and how long they may last.

BTW thanks for the inspiration as I have 2 articles due today and this gives me a topic for at least half of one of them.

[LCHIEN]

If you think of a battery as a pail and total charge as water.
Then current (measured in Amps or milliamps) is charge delivery rate.

A battery rated at 2500 mA-H can provide 2500 mA for an hour or 250 mA for 10 hours or 2 mA for 100 hours.
A pail with 2500 ounces of water can deliver 2500 ounces per hour for one hour etc. until the pail is empty.

mAH is the product of rate and time.
The pail I described is 2500 oz/hour X 1 hour. = 2500 Oz.
The capacity is really just a measure of how much it holds. Inthe case of a battery it comes down to total electrons.

The rating applies can be given to any battery... niCad, NiMH, Lead acid, or alkaline. The alkaline however cannot be refilled. the rechargeables can be refilled effectively, usually they quote 1000 fill cycles.

In reality AH are not totally linear, the way charge is stored chemically in batteries, using higher rates will not permit getting all the charge out so aH are most correctly specified at a particular Ampere drain (though most batteries do not specify that.)

Volts are the push or the force with which the Amperes are sent out.
The equivalent in a bucket is the PSI or head of the water. Drill a small hole int he bucket and apply pressure to the top, the more pressure the faster the water will go out the hole. Faster, slower, thats equivalent to the current of the battery, faster flow = greater current.