What the voltage will be when a 1.2 volt rechargeable battery is fully charged?

Question

when a 3.7 voltage cell phone battery is fully charged. it reads 4.2 volt. then what will the voltage of a 1.2 volt battery be when is fully charged? and is there an equations for these things? help please thanks

Answer 1

Depends on the cell chemistry.

However, for NiMH cells the charging voltage will be 1.4-1.6 Volts. A fully charged cell will be 1.35-1.4 Volts.

While you can charge using voltage as the charge termination indicator, a better method uses the cell temperature as the termination indicator. When the cell temperature starts to rise the cell has reached full charge. This method does not depend on the state of charge when commencing the charge or the rate of charge.

Cells should not be discharged lower than 1.0-1.1 Volts/cell. If you use cell temperature monitoring you can recharge at 1C rate (cell capacity per hour). If you use trickle charging the rate should depend on the self-discharge of the cell and should just replace the lost charge.

Answer 2

"To start with a cell is defined as a single vessel containing electrodes and electrolyte for generating current. A battery consists of two or more cells. NiCd/NiMH cells are rated at 1.2V for design purposes although they normally develop about 1.25V. Under full charge they require about 1.5V to 1.6V. They can supply very large amounts of current and display a remarkably flat discharge characteristic, maintaining a consistent 1.2V throughout discharge. The voltage then drops quite suddenly, and they are almost completely flat at 0.8V."

Your 3.7 volt cell phone battery is a battery of 3 - 1.2 volt cells, probably NiCd/NiMH, so charged it should be 1.45 x 3 or 4.3 volts, although again, when not being actively charged it will read 3.6-3.7 volts.

formula: No, it really depends on the chemistry of the cell.

Answer 3

3.7 volt cell phone battery tells me that it is Li-ion, which is the normal voltage for a single cell, i.e. not 2 or 3 cells put in series as with NiMH.  1.2 volt cell is normally NiMH or NiCd.  The full charge voltage cannot be compared as the chemistry are different.

NiMH charging voltage is in the range of 1.4-1.6 V/cell. A fully charged cell measures 1.35-1.4 V (unloaded).  While a charged NiCd cell measures 1.45 V.