when you hold down the help key you can check the battery level indicated by the VU/battery meter located on the right side of your OP-1.
the battery level is indicated by the LED array on the right side of your OP-1.all LEDs lit (including the red) indicates a fully charged battery good for around 8-9 hours of heavy use. The stand-by time is approximately 2 years.
to recalibrate the battery meter please do the following: disconnect USB, turn your unit on and leave it on until it turns off by itself. do not manually turn off the unit. this could take up to 18 hours. the unit is off when the screen has turned black.
after this, charge it fully using a computer or any standard USB charger. this can take about 2.5 - 6 hours depending on your situation. (the battery is 1800mA). this will recalibrate the battery indicator.