1. Can they always connect with power source for charge?
A: Yes, they can. There are built-in battery protection, means you can connect both TX and RX units to normal power source (DC 5V, 1A / 2.1A)all the time.
But a healthy usage habit will be more suggested to extend battery life, as well as save power. LED lights on RED during charging, then go off once fully charged.
2. Can't charge / hold charge any more?
A: Check with different micro USB charging cables or different charger adapters. If none will work, kindly contact firstname.lastname@example.org.