# Rechargeable 3.7V 500mAh Li-Ion Coin Cell discharge question

Discussion in 'General Electronics Chat' started by StealthRT, Sep 8, 2010.

1. ### StealthRT Thread Starter Active Member

Mar 20, 2009
223
0
Hey all, i was wondering if anyone knew the math to determine how long it would take for the battery to be discharged to 0%. Heres the stats:

500mAH running a 13.5mA chip.

How long would it take?

David

2. ### creakndale Active Member

Mar 13, 2009
68
7
500mAH / 13.5mA = 37H

creakndale

3. ### StealthRT Thread Starter Active Member

Mar 20, 2009
223
0
Hum, you sure about that, creakndale? I was thinking it was much higher than that?

I tried using this calculator but i wasn't sure if i was inputing the correct values:

Peukert Number Battery Life Calculator

Rated Battery Capacity: 500Ah
Discharge Rate: 3.6v
Peukert's Number: 1.1

and it says that the Full Discharge Time: 122.190 hours?

David

4. ### LTX71CM New Member

May 23, 2010
8
1
That's because your battery is rated at 500mAh and not 500Ah. For the purposes of that calculator your battery capacity is 0.5 Ah. Discharge rate is 0.0135 Ah. This gives you a safe 80% discharge time of 43.784 hours.

5. ### AMIT_GOHEL Member

Jul 13, 2010
67
7
Hello Devid,
one thing keep in mind that you can never discharge your battery fully and reach at 0%.
By calculation crakendel is right..

To get the proof you'll have to do a tiny experiment.
you might be having a cellphone.rite..
First fully discharge the battry(by playing game,listning music)Remove the battery and cheek the mAh written there,devide it by charger mAh, and you will get the charging time of the phone.put phone on charging..you will get your phone fully charged near to the theoretical time which you derived.
You can apply a same thing to finds the discharge time..

Regards...

6. ### Audioguru New Member

Dec 20, 2007
9,411
896
Like I said on the other website, a rechargeable Lithium battery is destroyed and might catch on fire if it is discharged below 3.0V. Usually the product has a circuit to pulse the power from the battery or disconnect it when the battery voltage drops less than 3.0V.

A Lithium rechargeable battery is regulated at 4.2V when it is fully charged. Then its voltage slowly drops and the load current also slowly drops as it discharges. You might not notice that a motor will slowly slow down.

I flew my electric RC model airplanes very slowly but the batteries were destroyed because I did not hear the warning circuit pulsing the motors when the battery voltages became low. One airplane's circuit cut the power to the motor when the voltage became low but then the airplane was far away and I nearly lost it.

7. ### eblc1388 Senior Member

Nov 28, 2008
1,542
102
43+ hours or more???

Under best condition, its 0.5Ah/0.0135A = 37 hours but it could be less because battery voltage drops and the unit being power no longer works.

You can't discharge a Li-ion cell down to 0V because you will kill it.

Last edited: Sep 9, 2010
8. ### LTX71CM New Member

May 23, 2010
8
1
That's not my math. I simply used the online calculator StealthRT linked to (http://www.csgnetwork.com/batterylifecalc.html) but using the proper values.

I made no attempt to verify the output, only to verify the input.

9. ### eblc1388 Senior Member

Nov 28, 2008
1,542
102
Fair enough.

This is what I've gotten from the calculator.

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10. ### LTX71CM New Member

May 23, 2010
8
1
I left Peukert's Number at the site's default of 1.1. Again I was merely trying to point out why the OP was getting hundreds of hours, he was using amps, not mA.

11. ### eblc1388 Senior Member

Nov 28, 2008
1,542
102
The Java calculator at that site giving an increased number of operating hours with battery of a higher "Peukert number" is simply wrong or programmed incorrectly.

Maybe it does not work for 13.5mA because this magnitude is hardly a "heavy" discharge rate for a 500mA battery.

The "Peukert Number", when applied, refer to case where a heavy discharge is put the battery. One would get less operating time in such case.

It is a factor that *Reduces* the time of useful discharge instead of the simple Ah/load equation. Come to think of it, if I'm applying 5A load to a 0.5AH battery, it is very likely that I would get much less than 0.1 hour of battery time.

12. ### StealthRT Thread Starter Active Member

Mar 20, 2009
223
0
Ah, well thanks for all the reply s and also thanks for posting the pic there of the calculator eblc1388. 37 (43 from the other forum, though) hours isn't all that bad really. I was hoping for more but maybe having it off every 30 seconds will prolong that time a little more instead of being on 24/7.

David