Based on the charging profile in the image, at 3.2V the battery would be in the constant current phase of charging. This phase occurs after the precharge phase and is characterized by the battery voltage rising steadily while the current remains constant. The transition to constant voltage phase happens at 4.2V according to the plot, which is after the voltage level of 3.2V in question.

The image shows a precharge phase, when is that necessary?

The precharge phase, also referred to as the trickle charge phase, is necessary when a battery has been deeply discharged below its recommended minimum voltage threshold. This phase applies a small, safe amount of current to the battery to gradually raise the voltage to a level where it can safely handle the higher current of the constant current phase.

Here are the typical conditions when a precharge phase is applied:

The precharge threshold (the voltage level at which the charger switches from precharge to constant current phase) is typically set by the battery management system (BMS) or charging IC (such as U2 in this project) and depends on the chemistry and recommended charging profile of the specific battery.

Based on your project description and the block diagram you've provided, let's perform a comparison to ensure your project encompasses all the necessary elements depicted in the block diagram:

Based on this analysis, your project seems to cover all major functional blocks presented in the block diagram. Make sure to confirm:

Ensure all nets are connected to their corresponding components as intended and that the boost converter, if present, outputs the correct voltages for your system's requirements.