The indication for full charge cell are follows:
The color plates on full charge is deep chocolate brown for positive plate and clear slate gray for negative plate and the cell looks quite brisk and alive.
When the cell is fully charged, it freely gives Hydrogen in Cathode and Oxygen in Anode, The process is known as GASSING. Gassing at both plates indicates that the current is no longer doing any useful work and hence should be stopped. Moreover, when the cell is fully charged the electrolyte is assumes a milky appearance.
The voltage ceases to rise when the cell becomes fully charged. The value of the voltage of a fully charged cell is a variable quantity. being affected by the rate of charging, the temperature and specific gravity of the electrolytic etc. The approximate value of emf is 2.1V or so.
Specific Gravity of the Electrolyte:
A third indication of the state of charged of a battery is given by the specific gravity of the electrolyte. We have seen from the chemical equation, that during charging the density of electrolyte decreases due to other production of water. Where it increases during charging due to the absorption of water. The value of density when the cell is fully charged is 1.21 and 1.18 When discharged up to 1.8V. Specific Gravity can be measured with a suitable hydrometer which consists of a float, a chamber for the electrolyte and a squeeze bulb.
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