This is equivalent to a 5A constant current source connected in parallel with a lithium battery constant voltage source connected to a load, such as a 3.7V lithium battery. If the load is less at 5x2.7 = 13.5 W, the battery. is in power absorption charging state. If the load is more than 13.5 W, the battery is in discharge state. This does not take into account changes in battery voltage. In fact, it mainly depends on the operating current of the load. If it is greater than 5A, the battery is discharged, and if it is less than 5A, the battery is charged. The voltage and current of the load have nothing to do with the state of charge. The only thing that matters is the battery voltage. When the battery is discharged, the charging voltage can be around 3V. When the battery is fully charged. the charging voltage is about 4V, and the direction of the charging current will not change.
At the same voltage, a charger with a large output current should charge faster. If the charging current is large, the chemical reaction inside the battery will accelerate and it is easy to reach the limit voltage. But the battery can't be too big, otherwise it would accelerate its aging and shorten its lifespan... If a charger with an output of 5 volts but only a few tens of milliamps of current charges a lithium battery, it won't is perhaps not the case. fully charged for a long time.