So I bought a brand new 12V battery to compliment the better of my two existing 12v lead acid batteries and dumped the older/weaker one just in case this had anything to do with the failure (although Steve assures me that the Powerlab will compensate for any weakness in the Pb cells and simply fail the test rather than going bang so I still feel the last power lab must have been faulty) and I also replaced all the 12v battery terminal connections with brand new bright and shiny connectors again just in case a bad connection had caused any sort of spiking.
Voltage spikes are the most likely cause of electrolytic failure so I am taking no chances, also I reduced my test cell to a single 20Ah EIG cell rather than 2 in series even though the powerlab should be well able to handle 2S of these cells (we had already done the power calculations to check we were not pushing it beyond the 1344W limit and again if we did try to it should just fail the test not explode!) I was not willing to take any chances this time and am going to stick to single cell tests despite the huge amount of time this will eat.
So to get the ball rolling proper I configured my BC168 balance charger to charge at 6S (8A) so I could top up 6 EIG’s at once and once I had the first six charged the ball really started to roll, it turns out that a single cell test takes around 28 minutes @ 40A to discharge and it takes the BC168 around 3 hours to charge 6 cells so all in all a pretty good balance I can charge 6 whilst I am discharging 6 (albeit one at a time) and then rotate.
So pushing hard to keep this turnaround going I managed to get 30 cells done in 1 weekend that is 1/10th of the entire pack so assuming I only get weekends to do it (I will be doing some in evenings) it would take me 10 weekends to complete the job.