I am quite new to batteries and charging them. I have a Polymer Lithium Ion battery (7.4V) and am about to attempt to charge it with a battery charger. The charger has a myriad of options from battery type, charge voltage, and current. I do not want to destroy the battery by attempting to over or under charge it. I peeked at a generic datasheet for LiO batteries and found an interesting charging plot.

The datasheet can be found here: DataSheet - see page 19.

enter image description here

What is going on here? The description of this plot writes that the maximum charging voltage is 4.2V (which presumably is for the battery they were using to collect this data).

Is this plot showing that at a charge voltage of 4.2V, the charge increases linearly for the first hour or so and then tapers off and the charge capacity of the battery is reached? Is this type of behavior governed by the controller inside the battery or does the battery suppress input current (like a charging a capacitor in an RC network)?

For a 7.4V battery, do we charge it at 7.4V? What are the differences between slow and fast charging (i.e. high or low input current)?

What are the side effects of charging at high current? Of course the battery would charge much faster, but does that shorten the life of the device?

enter image description here

  • \$\begingroup\$ What is the capacity of the battery? \$\endgroup\$ – Ignacio Vazquez-Abrams Feb 19 '14 at 18:56
  • \$\begingroup\$ It's a 7.4V, 2-cell, 1000mAH battery. This is all I know. I apologize if I am coming off quite naive. Here is the product: sparkfun.com/products/11855 \$\endgroup\$ – sherrellbc Feb 19 '14 at 18:58

Look closely at the top plot and you can see it is just applying a simple maximum current OR voltage scheme. Up to about .9 hour the maximum current (looks like about 700 mA) causes lower than the maximum voltage, so the battery is charged with that current. When the battery reaches the 4.2 V limit, the charger holds the voltage there and the current then decreases. Eventually the battery gets so full that the charging current tapers off to nearly 0.

The charger puts out either 700 mA or 4.2 V, whichever results in lower voltage (or current). The battery then decides the other of the two.

  • \$\begingroup\$ Thanks for the clarification on the plots. How do different charging currents affect the life of a battery? Put another way, what are the benefits and drawbacks of charging at difference currents (other than charging time)? \$\endgroup\$ – sherrellbc Feb 19 '14 at 19:08
  • \$\begingroup\$ @Sherr: The benefits of following the manufactuer's specifications is that the remaining specifications for the battery will remain valid, like it won't loose capacity quickly, leak nasty chemicals all over your electronics, or vanish into a puff of greasy black smoke. \$\endgroup\$ – Olin Lathrop Feb 19 '14 at 19:30

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