Give your battery a healthy boost
Check your battery’s output with a multimeter. Set it to 20V and then touch the red probe onto the (+) terminal and the black probe on the (-) terminal. Your bike needs to have 12.4V or more to start.
Charge it up
If the battery is below 12.4V, connect it to a charger before you try to start your bike. Some chargers won’t work if a battery is below a certain voltage, if this is the case you may need to replace the battery.
Connect the battery to the bike and switch on the ignition. With a multimeter connected, the voltage should drop then hold. If it continues to drop then it’s time to replace the battery for a new one.
Only replace a battery with one of the same performance. Reserve capacity is important because of parasitical drain from alarm systems. Also, buy a quality brand to maximise its life span.