Just got the battery, charged and tested and it is reading its recommended battery life of 680cca(it read 719cca)after three days the battery went flat and the lights started to its brightness, the dash lights weren't on.
My car has 20790 miles.
My car has a manual transmission.
I have seen batteries go flat after a day from a drain on the battery. You should have the battery recharged and have the system checked to see what is draining the battery. The alternator or some other electrical component could be at fault.
I have seen fuel pump relays stick and keep the fuel pump on after the key is off.
If you decide to get this fixed, consider YourMechanic, as a qualified professional can diagnose your draining battery and fix it accordingly. Good luck.
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