# Working out electrical characteristics of a device based on battery

Thread Starter

#### Gump

Joined Jun 7, 2010
57
Hello,

I have a small mp3 player, but I know nothing about its electrical properties, other than the battery. The battery has the following specs:

lithium battery Specifications:
1) Rated capacity: 120mAh
2) Impedance: <180 MOhm
3) Max. dimensions (D x W x L): 3*23*23mm
4) Max. operating current: 1C (110mA)
5) Weight: about 1.5g
6) Nominal voltage: 3.7V
7) Operating voltage: 3.7V~4.2V
8) Operating temperature: -40~ +80
So, I know the player uses 3.7V, but I can't work out the current it draws. I could work out the maximum current it could draw (assuming that the player is designed not to draw more than the battery) from the following line:

Max. operating current: 1C (110mA)

Although I don't fully understand it, is this saying that the device in theory wouldn't pull more than 110mA, but I'm not understanding the 1C?

Thanks for your help.
Gump.

#### crutschow

Joined Mar 14, 2008
24,056
1C is the battery current to discharge the battery in 1 hour. It is slightly less then the 120mA the Rated capacity would indicate due to battery inefficiencies.

If you know how long the player runs before the battery is discharged you can calculate the average current draw by dividing the battery Rated capacity by the number of hours. For example if it were 5 hours then the average current draw is 120mAh/5 = 24mA.

Thread Starter

#### Gump

Joined Jun 7, 2010
57
Hi crutschow,

Thanks for the comment, hope you don't mind me clarifying... So, what that's saying is I can pull 110mA and in 1 hour I would have discharged the battery? As for how long the device actually runs I don't have a clue. It's an OEM make and the chinese importer (got it from ebay) website says < 10 hours... Not too detailed, but on the other hand, it won't be drawing more than a couple of hundred milliamps so that'll let me accomodate other components accordingly.

Thanks,
G.

#### Smoke_Maker

Joined Sep 24, 2007
126
You could measure it with a multimeter, do you have one yet??, or can you use someones else's???

If you don't have one yet it maybe time to get one, it's indispensable.

#### K7GUH

Joined Jan 28, 2011
190
By all means, get a multimeter. You can get a cheap one for about $3.00 these days. They go up in size and price from there. If you'd like to pay the postage, I have a good large one I'll give you. It will fit into a medium flat rate box, which is less than$11.00.

#### thatoneguy

Joined Feb 19, 2009
6,359
Close to a CR 2032 coin cell.

But the dimensions put it at at CR2330
That is a 235mAH cell, the replacement, anyway.

CR(Dia)(Height in x.x form) So a 2032 is 20mm diameter, and 3.2mm thick

Rated capacity discharge is 200uA, 5mAmax, 15mA pulse

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