If A Diesel Generator Does Not Start

What if is possible that you give me your number?

Model 1506A 250 kva generator cranking but not start there is an ECU what is the problem?

Thanks for the vid, my battery shows around 12.3/4 volts but when trying to start it hardly turns it also it turns very hard. After that the battery needs to be charged again, this can happen up to 4-5times before it starts. Is this a battery issue or something else?