How to Test for a Dead Cell in Battery

battery charger

battery charger (Photo credit: Benimoto)

Car batteries have six individual cells. They all must work together to have the battery function correctly. Even one dead cell demands a battery replacement.

You can test for a dead cell fairly easily if you know what you’re doing. Always be careful of the sulfuric acid within a vehicle battery. When performing the test, wear rubber gloves and safety glasses. Keep the ventilation coming to avoid breathing any dangerous fumes.

  • Have a battery hydrometer handy. Since the best way to test for a dead cell is to check the specific gravity of each cell’s electrolyte fluid, you’ll need to compare its density to water.. Bottom line: a low specific gravity in one cell when compared to the others equals a dead cell.
  • Disconnect the battery cables and connect it to a battery charger. Charge it up to full.
  • After carefully removing the cell caps, insert the hydrometer tube into each cell.
  • Once the tube is full, read the specific gravity level. Battery cell fluid should ideally be 1.265, but older batteries may not meet this standard.
  • Read each cell’s specific gravity number. If you find one cell with a difference of more than 0.05, you’ve got a dead cell.

If you identify even one dead cell, replace the battery as soon as possible. This will avoid you becoming stranded–which always happens at the wrong place at the wrong time.

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