Evening Gents and experts!~
I had occasion to be at my local Hobby shop,(ok so its 70 miles away, I always make it a point to stop in when I can) I was talking to Bryan about batteries for elect. We talked a bit about state of the art and he was very interested in the CL aspect of it. When I mentinoed that I have a complete drivetrain less batteries this led to another interesting discussion, another gentleman was standing there that does some Beta testing (his words) for the Eagle tree data recorders, got good words about that, I thinnk he flys helecopters. Anyway to the point, they both recomended that instead of going with a single pack config as I have read here at 4200 mah, I should look at using two 2100 packs, their reasoning was that if you had a cell go bad, you only loos half the flight pack instead of the whole thing. I can see a certain logic to their comments and was wondering what the prevailing thoughts might be regarding this? I know that from one perspective it has the potential to complicate the mounting and installation issues. Any other thoughts?
thanks

I wouldn't (and don't) worry about cells going bad. In most cases you spend more money and gain more weight (due to more packaging material, connectors, solder, balancer tabs maybe even cell chemistry.....) Besides, most battery manufacturers have warranties to some extent.   

The only gains I can see is being able to space the individual packs apart for better cooling. In large packs the cells in the center can go bad prematurely from heat buildup. However, this is very rare and only seen in cases when the cells are pushed very hard. You may also get better fitment with two small packs in some cases?

You said you may be able to resuse some cells from the small packs and there is no reason why you can't do the same in a larger pack.   

For the record, I have used two small packs as one large pack, but ended up soldering the two together (making a single pack). If it works for you, go for it.

Hi Mark,

I second what the others have said. Our batteries are very reliable. I have been flying electric planes for the past several years, hundreds of flights, and I have never had an in flight battery failure. I have blown up one battery due to a charger malfunction, and I have ruined one when I dropped it on a cement floor, it hit on it's corner (battery swelled up, not good, ..... dumb, and dumber ;-)

Here is a better example of reliability. When I fly at my club field in Las Vegas I get to fly with my friend Mark Leseberg. He flys his 37% IMAC planes with electric power, while we fly ours with gas engines. BTW: Mark's elec. flys just as good as our gas planes, his 3D flying is amazing. He has never had a battery fail in flight, and his batteries work harder than ours do. We turn 32 x 12 props! I'm sure Mark flys over 1,000 flights each year, and most of them are electric.

As Alan said, we should be really babying these things @$200 ea. ! Like most of the guys, I always use a balancer, and the TP data port feed back system, and keep a flight log of every flight, and every battery's charge info. from each flight. ..... I also mount my batteries surrounded by rubber matting material, under the Velcro, to help protect them during the shock of my landings. ;-)