The Hobbico Field Charger MK II that I have will shut down with my unmodded 6EXA. It detects peak without measuring back voltage. I don't really know how it does that. It must measure input current. I heard it won't put in as much charge but it will work with diode protected TXs. This, along with the two pack capability, is the reason I bought it. It is the best $50 I have spent for field gear because I can fly as long as I want even with the low capacity standard 600ma packs or when I didn't get to slow charge either my RX or TX.