Battery’s dead? Why?

Battery is not a very important aspect for bikers who drive RX-Z, 125Z and Honda EX5. This is because the battery is only used for signal indicator, fuel indicator and to drain the excessive voltage from the magnet to it.
But, it is very important for those who use electric starter bike such as LC135, FZ-150i, Lagenda and scooters. The problem is the battery is always dead at the time when we needed it the most. Why is this happening?
There can be three basic reason of why the battery can be dead:
1. Battery itself is condemned (cannot retain the charge anymore).
Solution: Replace the battery.

2. The alternator (or cut-off) is damaged (cannot charge the battery anymore).
Solution: Replace the alternator.

3. The bike is not used regularly and used a lot in start stop condition. When this happen, the battery is drained more than it could be charged by the alternator.
Solution: Charge the battery and use the bike regularly. If not, sell the bike to the one who needs it the most than you.