Iphoen4 FM transmitter battery 1,With FM transmit function 2,Smart Li-ion polymer battery 3.smart LED indicator Iphoen4 FM transmitter battery 1,with smart monitoring system inside ... function when the voltage is lower than 3V.5,with battery capacity indication function in different capacities at 20%.40%,60 ... %,80%&100%6,with FM transmit function,and 4 FM transmit frequency(88.1/88.5/88.9 ...