I don't have a ton on jungheucirch experience but can tell you that no charging system or machine can operate without 24 volts...if they are separate batteries find the 4 that test at at least 5.2 at piece and run a series circuit to charger...see if charger kicks up voltage then...if doesn't after having descent batteries...issue with charger itself
On the one with contactor not closing verify 24 volts in and both positive and ground inputs sending in whatever is control voltage 12v or whatever...if all test good hit contactor gently when trying to activate...then hit drive motor gently one with work...that will tell you where the issue is
As for the forklift verify power when going forward at coil...then flip forward and reverse wires to see if drives