The battery is deeply discharged when its open circuit voltage drops below 11.6 V. Measure the open circuit voltage.
Electrolyte (mixture of sulfuric acid and water) in deeply discharged batteries, it consists almost exclusively of water, since the proportion of sulfuric acid is greatly reduced.
Note.
- The electrolyte in deeply discharged batteries can freeze even in slight frosts.
- Frozen batteries cannot be reused. Deeply discharged batteries are sulphated, i.e. the entire surface of the battery cells hardens. Electrolyte is not clean (transparent), and has a whitish color.
- If you charge deeply discharged batteries shortly after their discharge, then sulfation disappears.
- If such batteries are not charged, the batteries continue to harden and their ability to accept charging is severely limited. As a result, the capacity of the battery is reduced.