The battery charge status indication ND2730 is as follow.
1. During charge, RED LED lit.
2. When the charge complete one of following hhapen.
At previous model(ND2700), RED LED blink meant there were charge error.
Because of HW change, at ND2730, RED LED blink means charge complete too.
When charge complete, turn on the power then you can check the battery gauge to see how much charged.
The rechargeable Li-polymer battery inside ND2730 is consumables.
The charge capacity reduced about 80% after about 400 recharge cycles and decrease very fast after that. You may feel the battery does not hold power after 1 or 2 years use. In that case, change the internal battery to the new one. The internal battery shall be available at he shop you bought the ND2730.