all the codes on this truck less than -09 are what we call "static return to off" meaning they are related to the way the truck should start up. The truck shut down drive control. check the key switch wiring.
You really should get an experienced electric forklift tech to check your truck. (paying for a service call can be a lot less expensive than throwing parts at it). But to help your boss out, have an industrial battery company check the battery 1st. (it is a well educated guess) if the battery tests good, you are going to have to have someone that knows what they are looking at, eyeball the drive motor brushes and contactor tips.
My bet/W.A.G. is you have a bad battery and a load of corrosion under the battery.
5489 is hours most likely traction controller on hours, the other most likely hydraulic controller hours. error codes have a "-" in the first digit.
You might try and read the operators manual to see what the normal operation should be.
If you are going to check the wiring (or attempt any other work), make sure to get the drive wheels off the ground and disconnect the battery first. Electric forklifts do not use the frame as a path to battery negative, and have capacitors that hold enough power to move the truck, even when the battery is disconnected (they be dangerous).