There is more to a battery pack than just batteries. The way that the manufacturer bonds the cells is very important. The reason for this is that the vibration in the RC aircraft is pretty high which can cause poorly constructed packs to come un-bonded resulting in an open battery pack.. and you should be able to figure out what happens next.

Regarding checking battery packs frequently during a flying day, I told a story, actually a few times here on RCU, about my Venus II, which is a 90 size pattern plane. I have a pair of 1200mah NiMH packs in this plane. I operate them in parallel, each having its own switch and going to a separate channel on the RX. I also use Voltwatch on the Venus II. After two flights one day, and after checking the battery pack before and after each flight as I preach.. I had checked the battery packs (both.. the method is simple.. turn both off, then turn one on, check it, turn it off and then turn the second on and check it).

I checked both packs before the second flight, and all was fine. I flew for about 10 - 12 minutes, then landed. After carrying the plane back to the bench, I did my routine.. checked the battery packs again.. as I said, before AND AFTER each flight. When I checked the voltwatch, which monitors the packs, I found pack #1 in the green, and then pack #2 in the RED!!! So, I checked them both with an ESV. One read 6.1 volts, and the other read 1 volt, then the display on the ESV flashed a few times. I was totally surprized and thought that my ESV was bad, so I borrowed someone else's ESV and it read the same thing.

I removed that second battery pack and checked it again.. same thing. Fortunately, I had a spare battery pack, so I put it in the Venus II and recharged both batteries to make them both the same.

The voltwatch and my practice of checking battery voltages before and after each flight saved my plane. AND, what's applicable here is that the battery failed in flight. Checking after three or four flights would have resulted in a crash.

CGr.