Do you have a multimeter? If so, disconnect the battery(s) and check the voltage between the plus and minus. I don't know what voltage the original batteries are but as an example let's say they are 12 volts. If the voltage of the new batteries are low, say around 3-6 volts, the charging system may not "turn on" as they need to be a higher starting voltage. Maybe 9-10 Volts. If that is the case and you have a charger for your car battery (generally 12 Volt system) then you can charge to full voltage and start from there.
Just a thought.