you may need to get someone with experience in these units (or an electric forklift tech with a schematic) to check your battery hook up. this is not so much a 24 volt truck as a 2 section 12 volt truck that can use both 12 volt sections together as 24 volts for a faster travel speed.
my bet about the 'popping sound' is that you are blowing the circuit breaker inside the charger, and if you let it go, it will blow/burn out the circuit breaker.
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