# how to read battery spec?

I window shopped for a small size battery. On the battery specifications, there are:

• capacity(mAh) : 85mAh
• Pulse Current(mA) : 190
• Cycle Life(Times) : 300

What does Pulse Current mean? Does it means this battery can supply 190mA at a time? If there is no resistance between the terminals, can this battery supply power for 190/85 hour?

What is Cycle Life?

Do I have to connect a resistor when I operate the micro motor with 5v 500mA power source? [sic]

• You've not improved your formatting since the last question you've asked! Please avoid using line breaks in the middle of a paragraph. – Kevin Vermeer Jun 13 '11 at 11:50

First, read a bit on meaning of word pulse.

The pulse current is the maximum current that battery can provide. If the current goes higher, battery can be damaged and will probably start overheating. The missing part is definition of the pulse. Somewhere in the datasheet it should be mentioned how long the pulse lasts. The other part which is also important is continuous current. It is the maximum sustained current which battery can provide and is usually much lower.

Cycle life I believe means the number of times the battery can be recharged.

One part you also missed are definitions of power, current and amount of electric charge. The charge a battery can store is measured in coulombs. It is shown in mAh because of the relation between those units. $ampere=\frac{coulomb}{second}$, so when you multiply ampere by second, you get the charge. the milli part is because traditionally small batteries have too low capacity to warrant use of Ah (which is used for lead-acid batteries). So to calculate roughly how long the battery will last, you need to divide the total capacity by the current you will draw from the battery. So if you're planning to use 190 mA, you'll get around $\frac{85mAh}{190mA}\approx 0.44h$. Do note that the battery will most likely not survive such use, because pulse current is usually higher than continuous current, which you'll need to take into account if you want to use battery with electrical motor.

As for resistor part, well the best idea would be to control the motor using variable voltage to set the current. So yes, you can use a resistor to limit current going through the motor. Do note that the resistor will use some of the power provided by the battery.

• why isnt volatage mentioned here? Doesnt that include in the spec? – 0xakhil Jun 13 '11 at 8:01
• @0xakhil It does, but OP didn't mention it either and it's a whole field for itself which I didn't want to get into. Also it's much more related to battery chemistry than the capacity so I can't give specifics if I don't know the type of battery. – AndrejaKo Jun 13 '11 at 16:38
• I found in wikipedia that AA battery has a capacity of 2700mAh, while 9v (PP3) battery has a capacity of 565mAh. Isnt that weird? Check the comparison here: en.wikipedia.org/wiki/List_of_battery_sizes – 0xakhil Jul 9 '11 at 9:17
• @0xakhil No, it's not. There are no AA batteries. There are AA cells! The distinction is important in this case. The 9 V battery consists of 6 cells which are similar to AAAA cells and therefore have much smaller capacity. To reach the voltage, they are connected in series, so capacity of one cell is the capacity of whole battery. If you compare the size of AAAA cell and AA cell, you'll see that it's obvious why 9 V batteries have such small capacity. – AndrejaKo Jul 9 '11 at 10:23
• Are you talking about rectangular box shaped 9V cell? – 0xakhil Jul 9 '11 at 14:01