I think you're problem/was that the series of the 3800's you had were not really strong. In the beginning of the first 3800's series IB had some problems with the lifetime and venting.
Now the problem is solved with all the new series of 3800's and 4200's.
But remind, we made some intense testing on the IB's. Please do not discharge them bellow 0,7-0,8 volts, this will destroy the capacity of the cells. It does not take influence on the voltage, but runtime will be killed big time.
Our experience is a loss of 30-40 seconds!!
Also we made some tests on the GP 4300, but I do not want to start any discussion here again. Makes no sense, customers will make their choice!
Hope to see you soon Mathijs,