A bit more information to go with my battery posts, numbers 73 and 80.
There are two ways that a cell in a battery can fail quite quickly.
1/ Almost instantaneously is when the lead plates in a cell become detached at the tag that links the cells together.
Plates are roughly rectangular with a tag at one of the corners. According to the batteries rated capacity the number of plates in a cell varies, from about 5 to 9 for cars.
When the block of plates is placed in one of the 6 compartments in the case the tags stick upwards in a row.
The positive plate tags to one side and the negative tags to the other
A lead link is melted on to the tags fusing them all together. ( pos to pos, Neg to neg. )
These links are then joined together so that the total voltage along the length of the battery is approximately 12.6 volts.
( Each cell being close to 2.1 volts.--Six cells. )
2/ The second way a cell can die is when, due to vibration over several years of use on the car, some of the paste from the plate grid falls to the bottom of the cell and causes a short circuit across the negative and positive plates, rendering them useless.
If checked with a volt meter the reading across the battery will show around 10 volts.
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