[Sydney]

Hey blykins,

If you only had 12.4 volts before you started, that battery was only about 80% charged to begin with. Typically a fully charged battery should read somewhere in the 12.75 vdc range depending on the type of battery. If I remember right, an optima will read between 12.75vdc and 12.80vdc when fully charged.

You might try a different charger first to try to get the voltage up before you fork over money for a new battery. If that charger you have now says it's at 100% charged when the battery voltage is only 12.4 vdc then I would look there first.

Sydney