The adapter is marked with a nominal value of output capacity. It doesn't represent how to charge.
For example, a dry battery has a nominal voltage of 1.5V. It can light a small bulb or turn a small motor, but it's impossible for you to let it light up your lights. If you have a voltmeter, you will find that when it lights up the small bulb, the voltage is almost 1.5V. When you turn the small motor, its voltage is much lower, and when you connect it to your electric lamp, its voltage is almost zero.
In other words, when the output capacity of your adapter is less than 1.5A, the voltage is basically within the allowable range of nominal voltage. It is to convert 220V AC power supply to 7.2V DC power supply with output current less than 1.5A.
How to charge is determined by the circuit on the charging board. The size of charging current and cut-off voltage are determined by the circuit on the charging board. Generally speaking, the voltage of the power supply you add to the charging board is higher than the nominal voltage of the battery. As for the height, it depends on the tolerance of the filling plate. If it is a charger for charging various batteries, its withstand voltage is generally very wide. High 5V, 8V, some tens of volts are all right. If it is a special supporting charging board, for example, on a mobile phone or laptop. Then their withstand voltage range will not be wide.
From your description of charging, your understanding of electricity is not enough. You think the power supply voltage is constant. Do you want to lower the voltage by connecting a diode and a small resistance? Your transformation is wrong. Lithium batteries are extremely sensitive to overcharge and overdischarge. Without understanding the circuit, random transformation can only make your battery stop quickly.
