Error F 55

F55 is that your positive battery voltage is higher then the negative battery voltage.  Could be a bad cell in the negative pack.  Packs 1,2 are positive and packs 3,4 are negative.  If you don’t want to replace the batteries you would need to open all the packs and manually balance all the packs as close as you can. Depending on age I would replace all batteries and check voltage when you put them in so you can balance it. If they are new you need to go into service mode and make sure the voltage in the mode are correct. They can drift and the computer can think they are off and give you the error.  Battery voltage check is in the service manual. 

I am new to the forum. Please be patient. What are the battery specifications in these units. I do not want to pull out any batteries until I know I can get replacements.