4.5V is the voltage limit which is dangerous for the users and beyond which lithium-ion batteries are damaged. For this reason, all lithium-ion batteries have a protection circuit like the one in this picture. This circuit works in two ways: it prevents the voltage from exceeding 4.4V (which is a standard parameter compared to 4.5V limit) and it also prevents the voltage from dropping to a voltage below 3V beyond which the battery would deteriorate rapidly (in this case the safety limit is 2.7V beyond which the battery must not be discharged). In fact, when you reach 0%, the remaining battery, on the contrary, is around 5%. This was designed in order to prevent it from reaching its discharge limit voltage.
This protection circuit does not handle the recharge of the battery. It’s responsible for physically disconnecting the battery in case the voltage or current reaches beyond its safety parameters. The protection circuit won’t intervene when the battery is fully charged because it does not reach the safety parameter. Therefore, the battery remains connected to the power at high tension.
Topping & Trickle Charge
Charging circuits can be of two types: Topping and Trickle Charge.
Both take action at the end of the charging phase, which has in any case an initial phase at constant current and an ending phase at constant tension.
In case of the topping charge, once the battery reaches 100%, it restarts the recharge only after it has dropped to a threshold to bring it back to 100%.
The trickle charge, on the contrary, keeps the battery at the end-of-charge tension in order to preserve it at 100% while the absorbed current is almost insignificant (few µA as shown in this table).
"With iOS 13 and later, the iPhone uses machine learning for try to understand yours charging habits daily so that the Optimized charging option is activated only when the iPhone expects it to be connected to a charger for an extended period of time ", so Apple explains the new feature, which, however, has some critical issues.
Being on the level software and governed by machine learning is subject to many inaccuracies. It DON'T abbiamo fixed times or if we have a life hectic, for example, the iPhone will not never understand when we unplug the power supply from the phone and then we may end up with one charging blocked that will not be able to hold up until evening. Another example would be connecting the phone at the PC while working in the office, another parameter than destabilizes machine learning, and therefore the whole process.
Voltage VS Discharge Cycles
All charge controller circuits within smartphones, laptops, tablets and digital cameras charge lithium-ion batteries up to the maximum voltage supported by the cell. In most of the cases it’s 4.35V. This allows the maximum charge of the battery given that the consumers prefer a longer runtime.
However, charging the battery at maximum voltage tension will reduce its useful life and may compromise its safety. This chart shows discharge cycles in comparison to charge level. At 4.35V the number of discharge cycles of a lithium-ion battery is reduced by twice compared to 4.2V tension. Therefore, a lithium-ion battery should be charged at a lower tension than the maximum allowed in order to extend its lifespan.
It’s like relaxing a muscle after an intense workout.
We recommendapplying the ultra fast chargeonly when needed. A well-designed ultra-fast chargershould have the charging time selectionto give the userthe ability to choose the least stressful chargefor the allotted time. There figure compare la lifespan (number of cycles) of a typical Li-ion battery when it comes loaded and unloaded at 1C, 2C and 3C speeds. The higherthe charging speed, the faster the discharge cycles will decrease. There longevitymay be prolonged up to 500 cycles loading and unloading the of below 1C; 0.8C is the recommended speed. No apply the quick charge when the battery is cold or hot. Charge only at moderate temperatures and avoids to quickly load one old battery.
The "battery saver" apps
On Google Play Store you can find plenty of apps that monitor the battery state. However, they don’t disconnect the battery from the power when it reaches 100%.
Today there is an app that according to its programmers disconnects the battery from the charging state by setting a maximum charging threshold. However, in order to use this app ( which does not provide you with data and reviews on its performance) you have to change the system settings on your smartphone. In this case, the settings done by the manufacturer can only be changed via rooting by invalidating the warranty of the product. Not recommended as an action in case you are not a pro user and increase the risk of Brick your device (when the device no longer turns on).
Samsung even set up a “counter” to keep track of any signs of system tampering which can be detected even when you restore the original system setting.