Checking Battery rating

[Bob Schedler]

I have a number of 3.7V BRC 18650 Li ion batteries from Ultrafire, rated at 4200mAh - which I don't believe. So I have one of those natty little devices which can check this. I just put the batteries under load, and measure just about everything under the Sun - volts, amps watts, power etc. The only question is: what does the rating mean or claim? After discharge to zero volts (impossible)? Discharge to 50% of the volts? 75%?
Also, at what current should I discharge? 10% of the rating, ie 420mA?
Thanks for your help.

 

[Arouse1973]

Hi Bob. The capacity claim does seem rather high, maybe their cut off voltage is lower. The highest I have used are 3400 mAh from Panasonic. The capacity is measured using a fixed load and then timing how long it takes for the battery voltage to drop to a certain level, this is normally 2.5 Volts but I have seen specs saying 2.2 Volts. 10% of rated capacity for the discharge current is fine.
Thanks
Adam

 

[dorke]

Bob,
I think you should see this video...

 

[Bob Schedler]

Bob,
I think you should see this video...

I feared and suspected it! Never mind, next time I will pay more and then choose a Panasonic or Sony.

 

[Bob Schedler]

Hi Bob. The capacity claim does seem rather high, maybe their cut off voltage is lower. The highest I have used are 3400 mAh from Panasonic. The capacity is measured using a fixed load and then timing how long it takes for the battery voltage to drop to a certain level, this is normally 2.5 Volts but I have seen specs saying 2.2 Volts. 10% of rated capacity for the discharge current is fine.
Thanks
Adam

Thanks Adam,
Will use 10% discharging current. I think that lower than 2.5 volts may cause irreparable damage to the battery, according to various 'net claims.

 

[Alec_t]

Believe those claims. Over-charging or over-discharging lithium cells is dangerous. The better cells have safety circuits attached to prevent misuse.

 

[Bob Schedler]

[QUOTE="Alec_t, post: 1672951, member: 40611 ]Believe those claims. Over-charging or over-discharging lithium cells is dangerous. The better cells have safety circuits attached to prevent misuse.[/QUOTE]
My charger "seems" to recognise when the battery is fully charged, but to be sure, I constantly monitor the charging current. As I understand it, when the charging current is 0 mA, the battery is fully charged (?).

 

[Arouse1973]

Yes Alec, correct. But its the pack that has the circuit. Single cells dont as far as I am aware. But might be wrong. I only use them in qualified packs with circuits.
Adam