There are 5 common causes that caused a battery dead
Time (old age / time unused)
If your car’s battery is old, it will not hold a full charge well. Generally you should replace your car battery every 1-2 years. Besides, if you not starting the car for a long period of time the car battery will eventually dead off.
Hot or Cold
Temperatures
Cold or hot temperatures can cause lead sulfate crystals to build-up. The sulfate buildup can cause damage to your car battery if the car is left in such conditions for too long.
Human Error
You probably did this at least once in your life time – you left the headlights on or you forgot some internal lights and eventually your car drained overnight.
Bad Alternator
To recharge your car battery you rely on your alternator. If your alternator has a bad diode, your battery can drain. Even when the engine is turned off, the bad alternator diode will cause the circuit to charge and you end up with a car that won’t start in the morning
Corrosion
Corrosion can drain your car battery’s power, shortening its life. Corrosion of the battery is generally noticeable at the terminals.\
