When you get home with your dead board, turn it back on and ride it until it turns off. Repeat a couple times and your battery percentage should drop to 1%. Recharge your board to full and it should better sync your battery and app.
Behind that error message is a "usage" and "regen" percentage. If your board is fully charged, the first time you turn it off ride and you can compare the usage to the battery meter to see how they compare. 100 - (Usage-Regen) = Battery meter.
So if you board says it has 70% battery, you can compare that with other two. In a perfect world it might be something like 35% used but 5% regen (100 - (35-5) = 70%).