A car battery can develop an internal short, but symptoms such as a no-start or a battery that will not hold charge do not prove that is the cause. A discharged battery, a charging-system problem, a parasitic load or a poor connection can produce similar symptoms.
Does a low voltage reading prove a shorted cell?
No. Interstate’s battery-check guide notes that a reading near 10.5V on a 12V lead-acid battery can indicate either severe discharge or a shorted cell. One voltage reading is not a diagnosis. Recharge and test the battery using a method suited to its chemistry and rated CCA, following the battery and tester instructions.
How should a suspected short be checked?
If the battery repeatedly loses charge while disconnected or fails an appropriate load or conductance test, have the battery and charging system diagnosed. Do not open a sealed battery to inspect its cells. Replace it only after testing confirms it is outside the manufacturer’s service limits.
Sources: Interstate Batteries: 4-Step Battery Check; U.S. Department of Energy: Handbook 1084-95 — Lead-Acid Storage Batteries
