Jonesy -
Uggh. That's NOT cool. I'm going to recommend a couple things;
First -
Get in the habit of balance charging and CHECKING the per-cell voltage after the charge completes EVERY TIME. And then after use, before you recharge, check them with a stand-alone balancer like the one below and balance the pack BEFORE RECHARGING if any cell is more than .05V away from the others. The balancing circuit in a modern LiPo charger can only make up for SO MUCH of an imbalance; they only have a certain amount of time before the pack reaches delta peak. Balancing a pack that's as far out as yours can take hours.
Second -
Make double damn sure your charger is doing its job; charge your new batteries, then discharge them using a dummy load, NOT the "discharge cycle" in the charger. For my 3S packs, I use a single 60W headlight bulb; for 6S, use 2 in series. You need to monitor them with a battery tester like this one:
http://www.hobbyking.com/hobbyking/s...dproduct=34137
which will sound an alarm if the connected battery becomes imbalanced, as well as a regular battery minder like this one:
http://www.hobbyking.com/hobbyking/s...rm_2s_6s_.html
to tell you when the battery is done discharging. If you get through the discharge cycle on a new pack and all cells are within .1 volt under load, your charger is PROBABLY working properly. If not, the balance circuit is probably compromised. This tester is the one I have; it will alarm if battery balance goes more than .04V off on any cell, which is good for an unloaded battery. It will probably go off on one or more cells with the battery under load when the battery nears 3.3V per cell; this is normal.
There is an array of transistors and resistors in the balance circuit; those transistors can develop a leaky junction or even short out as a result of voltage spikes caused by sparks when connecting/disconnecting a pack, or even from a brand new pack with very low internal resistance drawing too much current from the balancing circuit. The worst part is, this can happen and the charger APPEARS to work normally; voltages appear normal at the end of the charge, and the only way of knowing is that batteries start to fail repeatedly in the same way.
I had a brand-new 4S 25-50C rated Nano-Tech kill my iMars charger this way; the internal resistance on it measured like 5 milli-ohms! I found after the first charge with that battery that subsequent charges never charged accurately on 2 cells; it had actually drawn enough current through the balance circuit to kill 2 of the inputs on the voltage monitor D-A converter. After that, I never charge at more than 2 amps on that pack; though I have charged as high as 6A on my 3S packs.
Right now, I'm in the process of rebuilding one of these:
http://www.hobbypartz.com/75p-t6-multi-charger.html
that I picked up off eBay for $17; the one channel that appeared to work seemed to charge normally to an even 4.20V/cell; it even tested right with my Power Analyzer. I would never have known there was something wrong with it if it weren't for the fact I left a battery connected which I had observed charge up evenly to approx 4.19V per cell just before I sat down to watch TV with wifey for a few hours; when I went to disconnect it, I found one cell had dropped to 3.9V. A little testing revealed it had a shorted transistor (about the size of a grease ant) in the balance array on that channel.
My point is this; if you're not checking the cell balance of your batteries EVERY TIME you charge (I do), one of your batteries could have damaged that cell of the balance array on both your chargers and you'd never know.
Too bad you're so far away; I'd be glad to charge your packs on one of my known-good chargers and give them a dummy-load workout... I'm not afraid of your batteries damaging my charger since I can fix it if they do anyways.
Actually... if you have a friend nearby who'd let you charge your batteries on their charger, the chance of harming a charger with a faulty battery is very small if you charge at 1A or so; I'd suggest you balance the packs, then try charging on another charger, and then double-check the voltage per cell with a power analyzer like the one I link above.
mnem
*adrift*