Test flights are generally conducted to obtain data, not to provoke 'incidents'.
All possible precautions are usually taken to minimize the risk of potentially uncontrollable situations.
Sorry HazelNuts39 I think we are at cross purposes here possibly due to my use of the word 'incident' to mean an individual occurrence or event out side of the normal operating parameters of the battery or charging system, I wasn't thinking of a catastrophic battery failure.
Without such an event they will have no more knowledge than they have now, hence my comment on how long do they keep looking for something.
What would be interesting to know is what instrumentation has been added to the battery pack and charging system to record the parameters.