According to the owner's manual, it is not fully charged until it stops flashing red. If it will not fully charge in 3 hours, you probably need to replace the battery, however, I am unable to locate a supplier that provides a compatible battery for your unit. You might contact Plantronics directly for a replacement battery. If it is less than a year old, you should be able to get a warranty replacement unit.
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According to the owner's manual, it is not fully charged until it stops flashing red. If it will not fully charge in 3 hours, you probably need to replace the battery, however, I am unable to locate a supplier that provides a compatible battery for your unit. You might contact Plantronics directly for a replacement battery. If it is less than a year old, you should be able to get a warranty replacement unit.