I've got the same DVT and it's great. When you are checking your batteries you want a meter that puts a load on the batteries. The batteries we use are a strange in ways. Using a standard voltmeter (without a load) it's possible that a battery can read good, but when a load is put on it (actually using it in flight) the voltage can drop to almost nothing and you lose your plane. The DVT puts a 300 Mah load on the battery pack it's checking. This is pretty close the normal usage load that will be on the pack during flight, and is enough to cause bad cells to drop to low voltage under a load. Very very good insurance.

As for how low. The actual lowest voltage is 4.8v. Each cell in a pack has a minimum voltage of 1.2v, and 4 cells times 1.2v equals 4.8v. (FYI, max voltage per cell is 1.5v. for a total pack voltage of 6v) The receiver is designed to operate from 4.8v and up. Below 4.8v and the receiver won't work properly. My rule of thumb when I fly is 4.9v checked with a load. Below that and I wouldn't fly. It's not worth risking your plane just to get a couple more minutes of flight in, IMHO. Better to go home, recharge, and fly again another day. I use 1600 MaH NiMH packs and I usually get 5-8 10-15 minute flights on a flying day. Plenty of stick time for me.

Hope this helps

Ken