Industry technical tips: Check out some of the biggest myths about rechargeable batteries

Activation of new batteries

Myth 1: New batteries should be activated through cyclic charge and discharge.

The truth: To be precise, the above statement is not a rumor. There is a time difference between the battery leaving the factory and reaching the hands of the user, which can be as short as one month or as long as half a year. For batteries with a longer time difference, their electrode materials will be passivated, so manufacturers recommend that the first-time battery should be fully charged and discharged 3 to 5 times to eliminate the passivation of the electrode material and reach the maximum capacity. However, manufacturers usually do not pay attention to remind consumers that the full charge and discharge mentioned here should not be deep discharge, but should be controlled at 5% to 8%. Otherwise, a new battery is likely to be scrapped.

“First three” charging

Myth 2: When you buy a new battery, it is best to charge and discharge it three times. The charging time should be more than 12 hours in order to activate the battery's maximum efficiency.

The truth: In order to reach the most perfect saturation state, NiMH batteries need to go through the "replenishment" and "trickle" process, which usually takes about 5 hours. The "constant current" and "constant voltage" charging characteristics of lithium-ion batteries currently control their deep charging time to less than 4 hours. Once fully charged, the protection circuit inside the battery will automatically stop charging, so this practice is unscientific and has no practical significance.

Someone once did an experiment with a mobile phone. After fully charging the battery with a travel charger, he switched to a cradle charger to confirm the battery's saturation. When he found that the cradle charger was still charging the battery, he thought that the battery had not yet reached saturation. In fact, this test method lacks rigor. The reason is that the indicator light of the cradle charger is not the only standard for detecting whether it is truly saturated or not. The reference voltage of the cradle charger is not necessarily equal to the reference voltage of the mobile phone. Therefore, when the mobile phone thinks that the battery has reached saturation, the cradle charger may not think so and still charge, but only it knows whether it has been charged or not.

Best Condition

Myth 3: As long as the rechargeable battery is used properly, it will reach its optimal state and maximum capacity within a certain cycle range.

For example, early nickel-metal hydride and nickel-cadmium batteries, if used properly and maintained regularly, will reach their maximum capacity at 10 to 200 cycle points (a nickel-metal hydride battery with a factory capacity of 1000mAh may have a capacity of 1100mAh after 100 cycles).

The truth: This statement is more common in Japanese batteries, and can usually be seen in the cycle characteristics diagram in their technical specifications. However, for the current mainstream lithium-ion batteries, this cycle peak phenomenon does not exist. Because from the time a lithium-ion battery leaves the factory to the time it is scrapped, its capacity is reduced with each cycle, and there has never been a phenomenon of capacity recovery. Some friends may ask that some ThinkPad notebook users can restore the battery capacity through deep discharge. In fact, that is just a false detection by the test software, and the actual capacity of the battery has not increased at all.

Do lithium-ion batteries have an optimal state? The answer is yes, and it is related to the changes in the ambient temperature. Generally speaking, lithium-ion batteries will perform very well in an environment of 25℃~40℃. However, their performance will be greatly reduced in low or high temperature conditions. For example, if you use a laptop outdoors in direct sunlight, it will not last as long as if you use it indoors.

capacity

Myth 4: For two batteries with the same nominal capacity (for example 800mAh), if one is actually measured to have a capacity of 860mAh and the other 805mAh, then the 860mAH must be better than the 805mAh.

The truth: Generally speaking, for lithium-ion batteries of different models (different volumes), the higher the capacity, the longer the service life. If we ignore factors such as volume and weight, of course the higher the capacity, the better. But this may not be the case for two batteries with the same nominal capacity (such as the example above). This is because the battery with the higher actual capacity is likely to have substances added to the electrode material to increase the initial capacity, reducing the substances used to stabilize the electrode. The result is that after dozens of cycles, the one with higher capacity decays rapidly, while the one with lower capacity remains strong. In order to reduce costs and expand sales, many domestic manufacturers often use this method to produce high-capacity batteries. Users will find that the working time is greatly shortened after half a year of use. In short, the price of increasing capacity is to sacrifice cycle life. It is impossible to truly increase the battery capacity without manufacturers playing around with the battery materials.

Battery Storage

Myth 5: If rechargeable batteries are not in use, they should be discharged before storage.

The truth: In fact, there are more than just the rumors mentioned above. Many people are confused about whether lithium-ion batteries should be stored fully or fully discharged. The answer to this question starts with its inherent defects, that is, the "aging effect". After a period of storage, even if lithium-ion batteries are not recycled, part of their capacity will be permanently lost. This is because the positive and negative electrode materials of lithium-ion batteries have begun their exhaustion process since they left the factory. The extent of aging is different at different temperatures and saturation levels, as shown in the table.

It can be seen that the higher the storage temperature and the more fully the battery is charged, the greater the capacity range. Therefore, for long-term storage of lithium-ion batteries, users should control their power to 40% and store them at a temperature of 15°C or even lower. As for nickel-metal hydride and nickel-cadmium batteries, this "aging effect" does not exist. After long-term storage, they only need to be fully charged and discharged several times to restore their original capacity.

Fully charged and then charged

Myth 6: When charging the battery , it is best to charge it for 12 hours after it is fully charged. This will help increase the battery saturation.

The truth: Under normal circumstances, a quality charger will automatically shut down the charging circuit after charging is completed. Without current, even if the battery is left on the charger for 10 hours, it will be useless. Currently, most mobile phone chargers have this design. Therefore, when the green indicator light is on, you can directly take the battery out and use it.