Hey, with this Controller can you jump it out of the circuit to bypass the box?

well if you know that the batteries are in fact good then the BDI may be bad. You can try adjusting it in the controller if that is a BDI wired into the controller and see if it changes anything. Or if the BDI is self contained adjust it with the trimpots on the back side of the guage and check for any change.
Otherwise the BDI or controller may just be faulty and needs to be replaced.

I have a truck with this issue. I have not resolved it yet but when I get some downtime I plan on tinkering with it. I believe its a setting that needs to be adjusted with the service port computer. I also have my batteries load tested every two years by my battery supplier. With a full report of voltages and remaining capacities.

depending on the age of the truck , if this BDI is a curtis the guage might not be self contained, it may be connected to a controller box.
Simply replacing the guage might not fix it, if it has the separate control box the guage hooks to then the box is probably bad or needs adjusting.
If it is a self contained guage then on the back of the guage there will be 2 small trimpots that are used to set the guage parameters according to truck voltage.

And then of course there is always the possibility that the battery might just be bad and needs to be load tested. Voltage readings alone does not tell the story on battery state.

Did you ever get a reply? I'm having the same problem.

Its an order picker 24 volt with an EV-100, let me know what other info would help. The forklift runs between 8-10 hours a day 5 days a week. Thats where i got my assumption that the battery was staying at a full charge. I will try what you suggested and see readings i get.