Denso BHT-8000 User Manual page 177

If the CU-8021 is bus-powered via the USB interface from the USB host (PC) or USB hub and the host
PC is in the suspended mode, then the CU-8021 cannot charge or discharge the battery cartridge.
If the host PC switches to the suspended mode when the CU-8021 is charging or discharging the battery
cartridge, then the CU-8021 will stop charging or discharging. When the host PC recovers from the
suspended mode, the CU-8021 will start charging or discharging again and resume counting the
charging time.
Note that if the CU-8021 is connected to such a host PC that cuts off the power to the USB line in the
suspended mode, the CU-8021 will reset the count of the charging time. When the host PC recovers
from the suspended mode, the CU-8021 will start charging and counting the charging time from zero
regardless of whether the CU-8021 was charging or discharging the battery cartridge. To prevent the
CU-8021 from getting affected from the suspended mode of the host PC, use the dedicated AC adapter.
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