until you gain access to the batteries to actually check them out thoroughly your just wasting your time. It sounds to me like the batteries are toast.

Find a way to move the machine, either a forklift or you can unlock the brake manually and get a few guys and push it to a position where you can get access to the battery tray. Steerijng it would be the only problem, there is no way to steer it without hydraulic operation. If you look in the operators manual which should be in the manuals box it shows you how to move the machine, unlock the brakes etc.

When you say it shows 75% i'll assume it's showing that on the charger indicator (not the battery guage). This would be normal if it is trying to still charge the batteries. But since you say the battery guage shows no charge it would be safe to say the batteries are more than likely the problem.