It’s better to replace the battery before it dies, rather than waiting until your car is disabled. Signs your battery is failing can include any or all the following:
Battery/alternator warning light is on or blinking
Engine cranks very slowly, or won’t crank (turn over) at all
Electrical issues, such as the interior lights or radio malfunctioning or working only sporadically
You need a jump more often than not
Lights won’t turn on
Battery case looks swollen
Even without any signs, it’s still possible to drain a battery overnight by leaving your lights on or leaving something plugged into the power outlet.