Concerning the BDI showing only one bar, the one gentleman mentioned all the connections for the voltage to go through and can drop because of one thing or the other. I was told a trick by one Crown technician that works easily for me. I hook up my car charger, which I can set for AGM batteries and connect it to 2 of the 6V batteries and it shows 12V on the charger. Then I use the fast charge for about 30 seconds and turn on the key switch. It's always reset the BDI for me.
I only have this problem on older batteries I have to deal with until our next fiscal year when we can order new ones. It doesn't happen that often with them, most always when the operators leave it charged overnight. Then it will complete the charging process and slowly lose a bit of voltage until morning when it's unplugged. I've asked the operators to try and avoid that, but they don't care, lol.
You need to replace both Conductor Cables.
Your WAVE has an extremely high number of hours on it. Over time, your mast control cables will start to break internally and cause issues. I have seen this on trucks with 2000+ hrs on them. Also, the battery display indicator is not resetting because the controller is not seeing reset voltage. If you have enough of a voltage loss the controller will not reset even with new batteries.
First, the battery display. Fully charge the batteries. Then, raise and lower it 5 or 6 times and place it back on charge. The moment the charger says complete unplug the charger and immediately key on the truck. This should reset the display. This means that you have too much voltage loss between the batteries and the controller. Take voltage readings of entire battery pack. Then take voltage reading at CA401-1 at the controller. 24.8 volts min at the controller CA401-1 is needed to reset the indicator to full. You should not have more than 0.5 volt difference. If you do then you need to trace all of the connection points and correct the voltage loss.
Second, the lowering issue. If you can lower it by using the lower switch on the service panel then it's not a bad hydraulic pressure accumulator. A bad accumulator can cause a velocity fuse to set on the older WAVEs. If you have tested your lower switch up on the platform and it is ok then you probably have a bad mast control cable. These are very difficult to replace and you want to be sure that is the problem. You could do that by tracing on the schematic and hooking a jumper from the lower switch on the platform to the terminal for the lowering solenoid. Just don't have it very high and make sure that you stay out of its path. It could very well be that bad mast cables are causing both of your problems, especially with a high hour WAVE.
These are some of the ways that I have used to diagnose problems on the WAVE. I'm sure that there are other ways to test. That's the good thing about public forums. Many different ideas can be shared.