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I am charging a 430mAh lithium polymer battery at 1C using BQ24232 charger IC (from Texas instruments). The charge terminates within 1 hour 20 min with battery voltage showing 4.17V. On research I came to know that it would take a little more than 2 hours to complete the charge cycle when charged at 1C.

Why does my battery charges so quickly at 1C?

enter image description here

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    \$\begingroup\$ 1C = full charge/discharge in 1 hour. Where did your estimate of 2 hours come from? \$\endgroup\$ – Cheibriados May 20 '16 at 12:06
  • \$\begingroup\$ And why would it take more than 2 hours? \$\endgroup\$ – PlasmaHH May 20 '16 at 12:06
  • \$\begingroup\$ 80 mins charging time for the battery of that size is perfectly normal. \$\endgroup\$ – soosai steven May 20 '16 at 12:32
  • \$\begingroup\$ @Cheibriados, I believe 1C means the charge current is 1 times the battery capacity. For example, the 1C charge current of a 2000mAh battery is 2 amps. The 0.5C charge current of a 3000mAh battery is 1.5 amps. \$\endgroup\$ – st2000 May 20 '16 at 12:43
  • \$\begingroup\$ @st2000, you are correct w/r/t C-rate, but my point is the same; 2 hours seems arbitrary and without knowing where it comes from, the question is nebulous. \$\endgroup\$ – Cheibriados May 20 '16 at 12:48
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Your cell is not charging more quickly than normal. Rather, the other battery in your graph is charging much more slowly than normal because it has high internal resistance so quickly reaches the CV = Constant Voltage phase, which means that the charge time will increase because more time is spent in the CV phase (at lower charge current).

Below is typical CC,CV charge for a similar capacity cell. Notice that the charge completes in 73 mins - close to the 80 mins of your 430mAh cell. Notice also that it stays in CC = Constant Current mode for 57 of 73 mins, about 79% of the charge, which is typical for a healthy cell.

enter image description here

Contrast that to the graph you supplied below, where the 1C charge quickly enters CV in about 12 mins of a 141 min charge, i.e. at about the 9% time mark. This is typical of a very unhealth cell with very high internal resistance.

enter image description here

The first graph is from the site lygte-info.dk, which has a large number of reviews of batteries and chargers. Perusing some of those should give you better intuition on typical (dis)charge curves.

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Battery charging is seldom considered an exact procedure. There are acceptable procedures to charge different battery chemistries. But in practice there can be many subtle variations. Consider your TI.COM chip. There are likely many internal registers designed to give the OEM developer a way to adapt the chip to the application. For example, the application may demand a quick charge time (i.e. 1C or more) in exchange for shorter secondary battery life. Or the application may be for a device which routinely connect to mains power. As mains is expected to be normally available, the charge time can be extended (i.e. 1C or less) thereby extending secondary battery life.

This is a good place to start to learn more.

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