Logitech says there is no software available for these headphones aside from the utility to update the firmware. They are simply plug and play bluetooth and this is what Logitech recommends for determining battery level. AFAIK there is NO way to get a visual representation of battery level in Windows.
Thank you for following up on your case, we request you to check the steps provided below:
Single press the Power button, when headset is ON:
LED will show green for five seconds, which means the battery is between 31% to 100%
LED will show red for five seconds, which means the battery is between 15% to 30%
LED will flash red for five seconds, which means the battery level is less than 15%