Fh = f'n hot battery. Overvoltage.
Usually comes when the battery is right off the charger.

I have had instances of vfc causing this. Rare for b+ sense wiring to bring this code up but it is possible.

What's the model?
We had some issues with this a decade ago on swing reaches. Found turning operator lights on for a it would allow a start up.
You may need new firmware/flashware to reset the parameters.

Not so, if it's at 36V static (Not being used) it needs to be charged.
Lead acid battery discharge is not a linear function, from nominal battery voltage (i.e. 36 volts) to zero. To put battery voltage versus charge state in perspective - a healthy, fully charged 12 volt lead acid battery will be 12.7 to 12.8 volts (high performance batteries even higher). At 11.9 volts, a 12 volt battery is effectively discharged. You can pull them lower than this (not much useable power), or if not charged they will continue to drop voltage, but this is where damage occurs. An 80% discharged battery (12 volt) measures about 12.0 volts. Multiply these numbers by 2, 3, or 4 for 24, 36 or 48 volt forklift batteries.

What type of reach, model? 38 volts...charger may be bad too. Should have no more than 36 volts after charge.