Best method to test battery life?

Question

Some middle school students I'm tutoring are trying to find a good way to test AA battery life. They're looking for something fairly automatic and high-drain so they don't have to be constantly pushing a button or anything. Would building something to run a small motor be their best bet or do y'all have a better suggestion? I have a small bit of electronics knowledge, but wouldn't be able to construct anything particularly elaborate.

Answer 1

Put the rated load on it and measure the voltage is the traditional way. The load and the voltage you can get from manufacturers web pages.

Probably about 100mA for an AA, which would be a 15 ohm resistor. Voltage limit will be somewhere around 1.2 volts, with anything below that bad.

The voltage limit would be measured by a comparator such as the LM339, and it could light a red LED if bad and a green LED if good.

Answer 2

battery tester

Answer 3

You can get a free datalogger from DATAQ (reg $25) which is a device that plugs into a computer serial port and enables it to take and record voltage readings automatically.   You do need to have an RS232 serial port on the PC or buy a USB to RS232 adapter for about ($25).

Attach your batteries to a flashlight bulb and monitor the voltage readings with the DAQ

Radio Shack sells battery holders, lamp socket and bulbs. I would suggest using a 1.2V bulb and a single AA battery.  You can adjust the load on the battery by attaching more than one light bulb either is series or in parallel.   You can use insulated alligator clip patch cables to make solderless connections easily and allow easy reconfiguration of your tests.

Answer 4

put them into a electronic device and see if it turns on.

Answer 5

l**k it. or put it in an mp3. it say how much is left

Answer 6

try shooting at it with a water gun

Answer 7

There is already a battery tester for small batteries, but I guess you aren't looking for a ready made method.  How about a small flashlight.

Answer 8

put it in your mouth

NOT!

Answer 9

Here's a scientific test:

Hook up a small motor and have the motor under a load (fan blade or turning gears). With an electrical tester, measure the amp draw while the motor is running. If your AA battery is 1000mAh (milliamp hours) brand new and the motor draws, say 50 mA, then the battery should theoretically last exactly 20 hours. A greater load will draw greater amps.

Answer 10

if u wanna naturally charge them put them in hot water lol

Answer 11

Battery LIFE?

Hmmm!

Or, do you mean battery potential?

The best indicator of a batteries potential (its ability to do work)  is the voltmeter. As a batteries internal electrolyte is depleted by use, the open terminal voltage goes down.

Any battery reporting for duty with less than 80% of its nominal votlage is subject to failure.

A GREAT way to test the CONDITION of a battery (fitness for use) is a handheld product made by a company called Midtronics. It is only useable on larger Amp hour rated batteries as found in automobiles. All you need to do is input the CCA rating of the battery into the tool , plug it into the positive and negative terminals, and press a button and "voila' good or bad in indicated with extreme fidelity.

http://www.midtronics.com/

Answer 12

Ideally, you would use constant current discharges for your cells.

There are battery analyzers available commercially.

<>http://www.powerwerx.com/product.asp?Pro...

I have no doubt something could be made up that would interface with a computer. It's really only about switching loads and measuring equipment.

<>http://www.lamantia.ca/>

Answer 13

Let's start from a AA cell datasheet. Performance varies a little by brand, but fairly consistent.

http://data.energizer.com/PDFs/alkaline_...

Bill R is right, use a resistor for the load. To size it, select the discharge current you want. Figure 6 shows draws at 3 levels; pick any one or another level. Perhaps your kids could vote on the current draw.

Look at figure 6 to estimate how long the cell will last:

at 100mA draw @ 23°C (room temp), cell capacity is about 2400 mA*hr. Use Capacity = Current * Time. So 2400mA*hr/100mA = 24hr life. Note that a simple resistor does not provide a completely uniform current. However, it mimics what real devices do, so that is good.

You can use the estimated life in planning your test, but expect the results to varies. Perhaps someone can take it home to let it run continually, or you could just run during the day. This will give a little longer life though, as the battery recovers somewhat if not used part of the time. I would have the kids estimate the time, then have them guess times, to see who gets closest.

Now, size the resistor using Ohm's Law:

Voltage = Current * Resistance

I would use an average of 1.2V to size the resistor.

So, 1.2V = 100mA * R

and, R = 12 Ohms. For power calculation, use worst case power, which is at 1.5V. By Ohm's law, 1.5V/12Ohms = 125mA.

Since power = voltage * current,

power = 1.5V * 125mA = 0.19W. So, 1/4W or more resistor should work.

Now, looking at figure 5, you see that the voltage drops quickly once it hits 1.0V, as the cell is about dead. Most devices work down to 0.9V, which is why they use 0.9V under the title in Figure 6. So, I would use 0.9V for the limit.

This can be measured with a digital multimeter. Once voltage drops to 0.9V, test is done.

Good luck!