It's lucky you awoke when you did and discovered the problem going on right next to you. The failure of this unit may not neccessarily indicate that it is dangerous however. As with all electrical apparatus, it is liable to fail at any time be it new or old, it is the nature of the beast as it were. As you are aware with any electrical equipment ie, tv radio and anything containing electronics, it can fail simply by failing to operate or in the opposite extreme, even catching fire. Charging and discharging batteries is an area where I would strongly advise a monitoring schedule as it is an arduous process for both cargers and batteries under certain conditions and as there is a high degree of current available, the propensity for catastrophic failure of one or the other is higher than that of say ,your transistor radio which will simply fail to work.
So the advice is, regardless of quality, fused lines, size of batteries etc etc, one should always keep a weather eye on batteries and chargers whilst charging or cycling is in progress. I have seen a number of failures occurr on the best of equipment over the years.
The fact that you had problems with the supplier is however, a different story, having a problem with the gear is one thing, but the measure of a good company is not how quickly they supply you with stuff, but rather how effectivly you are dealt with when you have problems.