We now design electronic products, many times also use lithium battery power, like mobile phones or tablets using lithium battery power, familiar with the knowledge of lithium battery capacity, perhaps for the use and design of lithium battery power including the design of battery charger, it is necessary. Now many people who pay attention to lithium battery discharge, have such experience, is when the lithium battery from full voltage 4.2v discharge to 3.7v, time is very long, but once over 3.7v discharge quickly, yes, it is true. Read some lithium battery materials below, give you a summary.

First, said the battery discharge platform, which refers to fully charged lithium battery in the discharge, the battery voltage change state. Battery constant discharge of electricity, battery voltage to go through three processes, namely decline, stability, and then decline, in these three processes, the stability period is the longest. The longer the stabilization time, the higher the discharge platform. The level of discharge platform is closely related to the battery manufacturing process. Because each lithium battery manufacturer's market positioning is not the same, different technological means, the control of the discharge platform is not the same, the quality is very different.

Generally speaking, a lithium battery of 18650 has a full voltage of 4.2v. When it is discharged at a current of 1C to 3.7v for 60 minutes, then we can say that the battery's capacity is 2200mAh. During this period of time, according to the characteristics of the rechargeable battery, the following formula can be used to better understand the relationship between battery capacity, voltage, current time and discharge platform:

Capacity (C) = discharge current × battery discharge platform time

For a 2,200mah 18650 lithium battery, 1C to 3.7v takes an hour.

Capacity (C) =2200mA× 1h =2200mAh

Then the problem arises. For better lithium batteries, when we do product testing, the voltage drops rapidly after 3.7v, so the amount of power released in a short period of time is very small. On the contrary, when a bad battery discharges from 4.2v to 3.7v, the voltage drops rapidly, while after 3.7v, the voltage drops slowly. This kind of battery has poor performance and low capacity in general. So the discharge platform of good lithium battery is 3.7v.

In general, under the condition of constant voltage, the charge voltage is 4.2v, the current is less than 0.01c, stop charging, and then put it on hold for 10 minutes, at any rate of discharge current, discharge to 3.7v, the battery discharge experience a length of time, is an important indicator to measure the quality of the battery. However, do not blindly pursue a high platform, sometimes the platform voltage is high, but the capacity decreased, because, under different multiplier conditions, the platform voltage is different, therefore, the platform problem should be considered in many ways. Only when the capacity is high and the specified voltage lasts for a long time can the battery be considered truly good.

What is the discharge rate?

Discharge rate F: [1/ hour], which means "charge (discharge) rate of N hours, often only say" number ", not the unit; F is also called "charge (discharge) rate in N hours", F=1/ (N hours),

I= 0.1x [1/ (N hours)] XC

For example, when the battery capacity is 2200mAh, charge with the current of 0.1c, equivalent to clear: the charging current of the battery I=0.1 [1/ hour] X2200 [milliampere-hour] =220 [milliampere-hour]

With the aid of the lithium batteries battery capacity and discharge platform above understanding schematic diagram, can better understand the rechargeable battery capacity and battery discharge platform, also can saying is to measure high power battery working time, two battery capacity is the same, the same after a full charge assumptions at the same time from 4.2 V to 3.7 V, but a long time, a time is short, time is long battery high platform, is the time of high voltage long working hours, such as the two batteries for cellphones, standby time is the same, but the two phone call together, platform time long battery notice, Battery talk time with short platform time will be short

Second, in addition to understand the lithium battery power management monitoring is also very meaningful.

For example, currently, there are two ways to monitor the charge of rechargeable batteries.

Method for measuring battery voltage. When the charger is charging the test battery voltage, when the voltage reaches the specified voltage value is considered full. For example, when the voltage of lithium battery is charged to 4.2v, it is considered full. The accuracy of the voltmeter to detect the voltage should be plus or minus 1%. Because lithium battery overcharge to damage. If you want to monitor the battery charge and discharge, the book has a very mature circuit can refer to, if only to measure the words that is easy to do, according to the capacity of the load resistance, discharge with standard discharge current discharge, then detect voltage, as long as you can achieve or close to the nominal discharge time on the line.

This method of measuring battery voltage has many shortcomings. For example, for batteries produced by different manufacturers, the relationship between open circuit voltage and capacity varies. The advantage is low design cost.

Another common way to monitor battery remaining capacity is to estimate the battery remaining capacity by measuring the net charge flowing into/out of the battery and estimating the battery remaining capacity by measuring the battery remaining capacity in places that require more accurate battery capacity. Integrate the total current flowing into/out of the battery, that is, find the area under the curve in the figure, and the net charge is the remaining capacity. This method of calculating battery capacity is currently considered to be a more accurate method of calculating battery capacity. Of course, the design cost is also relatively high.