Battery’s fail for a number of reasons:

  • Heat
  • Age
  • Manufacturing faults
  • Poor battery terminals
  • Poor charging time.


It is said that a batteries efficiency to deliver power when cold is not as good when warm, however a battery that is overheating causes the electrolyte (batteries water)to boil, when the electrolyte boils and the level n the battery goes down there is less electrolyte in the battery to charge, the battery then has a shorter cycle. A constant charge and discharge of a battery with a low level of electrolyte causes the internal plates to become fatigued and break down quicker.


The age of the battery is the most common failure in the automotive industry, with a so many drive cycles and the constant load on the battery with so many electrical components in the vehicles today, its no wonder that batteries don’t last as long as they used to.

A battery’s age can be explained in various ways, one way we explain to customers is when a battery is new its like a full cup of water, with a full charge, as the battery ages the water in the cup goes down subsequently amount of charge the battery can hold goes down, for example if the full cup of water took 6 weeks to fully discharge with the vehicle just sitting in the garage, as the battery ages the cup of water goes down, so at half life with half a cup of water the battery might last 3 weeks just sitting in the garage. so when the battery is almost dead the charge wont even last over night. which will be when you know you need a new battery, early signs might be if you don’t start the vehicle over the weekend and you find it hard to start. if you think the battery is starting to fail we have tests to check the internal integrity of the battery.

Manufacturing faults

Faults lie in the internal structure of the battery, that is how the plates on the inside of the battery are connected to the outer terminals etc, if the batteries plates become eroded and short or the plates become dislodged and broken you have an open circuit battery, and will usually have the symptom of no power at all when going to start.

Poor battery terminals

Battery terminals are the main connection between the battery and the vehicle, the most common problem with the battery terminals is they build up a white acid around the terminals, this layer builds up a non conductive material between the terminals and the battery posts. the charging system then has to work over time to over come the poor connection subsequently causing an over charging battery which also causes the battery to over heat and fail sooner.

Poor charging time.

Charging time of a battery when half charged can take up to an hour of driving to fully charge the battery back up to optimum voltage level, when a vehicle is constantly driven short distances, it takes more battery life to start the vehicle than what is being put back in after the start, doing this time after time the battery is going to need a good drive to bring the charge level back to full.
Batteries are often changed when the battery will not start the vehicle, however the battery might just not be charged,  a full battery charged should read 12.6 volts as there are 6 cells to a 12volt battery, and to each cell there is 2.1 volts which equates to 12,6 volts when fully charged.
Battery voltage is not always a true indicator of a batteries health, but when checking why the battery has failed it is a test that should not be over looked.

Below is a table on battery voltage and charge level

Battery Voltage Explained

The open circuit voltage, is measured when the engine is off and no loads are connected. It can be approximately related to the charge of the battery by:

Open Circuit Voltage (12 V) Approximate charge Relative acid density
12.60 V 100% 1.265 g/cm3
12.45 V 75% 1.225 g/cm3
12.24 V 50% 1.190 g/cm3
12.06 V 25% 1.155 g/cm3
11.89 V 0% 1.120 g/cm3


More information about batterys

Why batterys fail
Battery maintenance
Battery Tests
Battery Technology