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How to charge lead calcium batteries

Updated February 21, 2017

Vehicles use lead-acid batteries to provide a 12-volt power supply. Lead is a very soft metal so it must be strengthened by adding other chemicals. Calcium not only hardens the lead but also reduce the production of hydrogen gas when the battery is charged. In the early 1970s, lead-calcium batteries were installed as "maintenance free" batteries because less hydrogen gas resulted in the electrolyte lasting much longer. Lead-calcium batteries needed to be charged at a higher voltage, almost 15 volts and with a special "Type IU" charger.

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  1. Disconnect all the leads attached to the battery. Place them somewhere where they cannot drop back onto the battery terminals. With the leads positioned out of the way, use a cloth and a wire brush, if necessary, to clean any dirt and corrosion from the terminals until the metal shines.

  2. Check the level of electrolyte in each cell. Remove the vent caps on the top of the battery and use a flashlight to check the level of the liquid in each cell. If the tops of the metal plates are above the liquid surface, check the manufacturers' guidelines, and then top up the cell with battery water or deionised water. Replace the screw caps, but don't fully tighten them.

  3. Ensure the battery charger is not connected to the electricity supply.

  4. Attach the battery charger leads to the battery terminals. The red positive lead goes to the positive terminal, and the black negative lead to the negative terminal.

  5. Connect the charger to the power supply, and then switch it on. Leave the battery to charge, checking occasionally to ensure it is not hot or making bubbling noises. When the charger indicates that the battery is fully charged, switch off the charger, remove the charger wires and tighten the vent caps on the top of the battery.

  6. Tip

    Clean the battery terminals with a stiff wire brush until the metal shines to ensure a good contact between the battery and the charger. Check the battery frequently while it is charging, and disconnect the charger as soon as the lights or charge meter indicate that charging is complete.


    Never over charge a battery. Bubbling and hissing sounds indicate that the electrolyte is boiling. This damages the battery and may cause it to explode. Remove all jewellery and metal watch straps before handling batteries. Touching the terminals with metal jewellery can short-circuit a battery and cause severe skin burns. Batteries contain strong acid. Do not spill the electrolyte or get it on your clothing.

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Things You'll Need

  • 15-volt "UI" battery charger
  • wire brush
  • old cloth

About the Author

David Robinson

David Robinson has written professionally since 2000. He is a Fellow of the Royal Geographical Society and the Royal Meteorological Society. He has written for the "Telegraph" and "Guardian" newspapers in the U.K., government publications, websites, magazines and school textbooks. He holds an honors Bachelor of Arts in geography and education and a teaching certificate from Durham University, England.

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