Specifications

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be used as an alternative. Finally, if none of these methods are ever utilized by the
charger as a shut off point, then an absolute timer can be used to cut off the charge and
prevent over charging. All of these methods combined, though complicated to
implement, would be the most ideal way to monitor when the nickel-metal hydride
battery has reached its maximum charge.
Figure 10 - Lithium Ion Battery Charging Circuit
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Above is an example of a lithium ion battery charger. Unlike other batteries, lithium ion
batteries‟ charging and discharging process is not a chemical reaction. Instead, it is
attributed to the movement of energy between anode and cathode inside the battery.
Despite this fact, however, lithium ion batteries, just like all other batteries do still
experience performance loss over time.
Lithium ion batteries are less complicated than nickel-metal hydride batteries when it
comes to charging, and are more similar to lead acid batteries. The lithium ion batteries
differ from lead acid batteries in the fact that they do not have a float charge stage and
the cut-off voltages of lithium ion batteries are more strictly set. This is to prevent
overcharging, which would be catastrophic for the lithium ion batteries.
Similar to lead acid batteries, the initial bulk charging stage of lithium ion batteries will
charge the battery to about 70% capacity. This is done at a charge rate of 0.5C to 1C,
and the lithium ion batteries generally have a charge time of three hours. These
batteries are considered full once the threshold voltage has been reached and the
current drops to 3% of the rated current. Another method to determine if a lithium ion
battery is fully charged is to monitor when the current levels off, as elevated self-
discharge may prevent the battery from reaching its threshold voltage. Below is the
current and voltage signature of a lithium ion battery in its charging stages.