The BDI "code" you are seeing stands for Battery Display Indicator. This is normal and should appear normally. The number displayed after the BDI message indicates the battery percentage.
If it doesn't want to move in one direction it most likely has to do with the handle and not the batteries. The best way to test the batteries is to place your dvom leads into the main positive and negative cables. You should see a voltage of >24v. Then while watching that value, lift the forks fully and see how far the voltage drops. If it drops more than 15% then most likely one or more of the batteries is dead.
Otherwise to solve the issue you will have to dive deeper into the issue to find the cause.
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