Battery charging is phased, from 0% to 90% (this is according to the battery will become) or so is constant current charging, that is, the voltage increases with the battery voltage.
Then enter the constant voltage charging mode, the voltage is slightly higher than the final voltage of the battery, the current will gradually decrease. Finally, it enters the trickle charging mode, and the small current maintains the charging state.
The standard 80% is because the battery has no absolute full concept, and the charging speed will decrease exponentially as the degree of charging rises.
0-80% will be fast, and then 80-100% [100% as defined by the charge control system] will take longer. And that's a high current charge. The benefit is simple, charging speed can be much faster. The disadvantage is that the battery heats up seriously, affecting the life of the battery pack.
Lithium battery charging current is too large will also produce gas accumulation and other problems. Ordinary charging can effectively extend battery life.
One example is Nissan's Leaf electric car, which has a battery life expectancy of about three years if it is only used for quick charging. If you use ordinary charging, the life can be doubled to 5-6 years if the discharge is half full. This is the point of ordinary charging