Is your car struggling to turn over when you turn on the ignition? You’ve heard about bad cells and suspect that it might be the issue with your battery but are not sure what signs and tests you need to do to confirm if it is the case or to rule it out.
This post explains the common signs you may experience if a car battery has dead cells, what tests you can do to check if indeed it is the case, and if you can and should repair a battery with a bad cell.
What Shows that a Car Battery has a Dead Cell(s)?
#1. Slow cranking or failure of the car to start
If a battery has a dead cell(s) then it will not be able to supply the necessary voltage and current to turn the engine over or even when it is able to, it may require several attempts or even fail altogether.
Note that slow cranking or failing to turn over in itself does not confirm that the battery has dead cells as it can be caused by: a discharged battery as a result of parasitic drain, self-discharge of the battery, or even loose battery cable connections.
#2. Failure of the car battery to attain a fully charged battery of 12.7V
The car battery voltage remains under 12V even after charging with an external car battery charger.
For example, the voltage of a car battery cell fully charged is about 2.11V (from 12.7V of a fully charged battery divided by 6 battery cells).
If one of the cells is dead or shorted, then the maximum voltage the battery can attain is only about 10.5V (5 x 2.11V). If more cells are dead then the voltage will be correspondingly lower.
How to Confirm that a Car Battery has Dead Cells
#1. Use a good quality portable battery tester or take the car battery to a reputable auto parts store for testing to confirm its health.
#2. If you’ve got a flooded lead acid battery, you can use a hydrometer to check if the car battery has dead cells or not.
Use the hydrometer to compare the recommended specific gravity values by the battery manufacturer against actual readings taken with a hydrometer.
You may need to correct the reading depending on the surrounding temperature. Consult its owner manual on if and how to make the adjustment.
Causes Dead Cell(s) in Batteries
There are several possible causes of dead cells in a car battery
#1. Deeply discharging the car battery repeatedly can lead to damage to the battery cells
#2. Shorting the car battery posts for example when connecting or disconnecting battery terminals. The battery can suffer damage from supplying excessive currents.
#3. Subjecting it to excessive charging currents beyond the recommended charging current levels. If the car battery remains uncharged for a long time below typically 12.4.
This can also lead to battery damage. And sometimes, batteries just develop dead cells with time and usage and eventually fail in spite of your best efforts.
What to Do if a Car battery has a Dead cell(s)?
In my opinion, you should replace the battery. It is probably not worth the effort in my opinion to attempt to recover it.
For the safety and peace of mind of knowing you have a reliable battery, I’d advise that you replace the battery with a new good quality battery.
Closing Thoughts
A battery with a dead cell will noticeably attain a battery voltage of about 10.5V or lower even after a full charge.
To confirm whether it is damaged or not, use a good-quality portable tester or take it for testing at an auto parts store.
Dead cells and damage to the battery can be caused by deep discharge, overcharging it, or even leaving the battery uncharged for a long time to mention but a few.
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