Batteries

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Mohamed Najiullah

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I want to know a few certain things about battery terminologies

1. What does Ampere Hour or Milliampere hour mean? For example my cell phone battery says that it has a capacity of 950mAh.. A NiMH battery has a capacity of 2000mAh.. What does it mean? Does it mean that the battery can supply 950mA for an hour? And if it does what happens after one hour? Is the battery completely discharged?

Well-Known Member
I want to know a few certain things about battery terminologies

1. What does Ampere Hour or Milliampere hour mean? For example my cell phone battery says that it has a capacity of 950mAh.. A NiMH battery has a capacity of 2000mAh.. What does it mean? Does it mean that the battery can supply 950mA for an hour? And if it does what happens after one hour? Is the battery completely discharged?

It means in theory (theory is the key word) that the battery can deliver 950 mA for a period of 1 hour to a load. However that isn't quite true. Much of this depends on the type battery, battery composition and the temperature. Depending on battery type it is dead when its voltage drops to a certain level under a load.

In theory a battery rated at 1 Amp Hour should be able to deliver 1 Amp for 1 Hour to a load but that isn't going to happen in reality. That same battery may deliver .1 Amp to a given load for 10 hours before its output voltage falls to a given point under load. All of it is pretty much relative.

With the same thinking it means a 1 AH battery should be able to deliver 10 Amps to a given load for 6 min and that isn't going to happen.

The AH rating can be useful in design planning but is not an well defined variable. It is a guideline and that is about it. This is a condensed explenation and doesn't begin to get into the variables including battery age or the number of charge / discharge cycles on the battery. There is much more to it.

Ron

Mohamed Najiullah

New Member
I've connected 4 NiMH AA cells.. Each of these have a rating of 1.2V and 2000mAh.. So a collective o/p of 4.8V in theory.. What would the practical o/p be?

audioguru

Well-Known Member
I've connected 4 NiMH AA cells.. Each of these have a rating of 1.2V and 2000mAh. So a collective o/p of 4.8V in theory.. What would the practical o/p be?
Look on the website of a Ni-MH battery manufacturer like Energizer. They have detailed datasheets for every battery cell. They also have a battery applications manual (charging and discharging details).

They sold AA Ni-MH cells that were 2500mAh but now they sell Ni-MH cells that hold a charge for many months and are 2450mAh. They sold 2000mAh cells many years ago so maybe your cells are very old?

The graphs on their datasheet for AA Ni-MH cells shows the voltage slowly dropping with various durations when the current is changed.
The mAh spec barely changes when the current is changed. They supply 2.5A very well.

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k7elp60

Active Member
mAH or AH is the capacity of the battery, just like liquid measurements like milliliter and liter. With batteries the capacity depends upon the discharge rate and it can vary between battery chemistries. For example sealed lead acid batteries the AH capacity is based on a 20 hour discharge rate. If you try to discarge this type of battery at is AH capacity it will only last about 1/2 hour. Connecting the same AH batteries is series increases the output voltage but the AH remains the same.

Mohamed Najiullah

New Member
Supposing I start the discharge when the battery is half full.. What would the o/p voltage be? Will it still be 1.2 V?

audioguru

Well-Known Member
Simply look at a battery manufacturer's website and see the datasheets.
Energizer shows a Ni-MH AA cell at various discharging currents.

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