I have used them and they are A good little item to have on board. I still have A couple in my older planes and have A couple of units in my box. I have gone to 6v in all my newer planes and when I got mine they only went up to 4.8, now they have them for both but I'm too cheap to buy them. Even with them on board it's still A smart thing to check the voltage before each flight. I like them and when I break down and buy some more I will start using them again.