Continuous operation is not possible with me

This device makes the vehicle voltage in a car 8 volts. But unfortunately not in continuous operation. For occasional post at the higher transmission power on Boafeng (with about 4 W), to dim the display to from. This happens but send only after mehfachen. Anyone who wants to test it, so you should send often with TXP High. The warmer the battery eliminator is, the sooner the problem occurs. I have test times as a connected power supply and the simulated on-board voltage (13,8Volt) measured at the output voltage 8Volt. While the voltage of the power supply remains the same, the 8Volt supply voltage drops to below 5.8 volts at Baofeng. For comparison, a battery has 7.4 volts. This I have tried with two Boafenggeräten. The result is always the same. A friend reported precisely the same problem. Therefore, unfortunately, I also only 2 stars.