This
situation arises when the system is allowed to discharge below the
voltage necessary for the Battery Management Unit (BMU) to restart and
stay on. In many cases, it is possible to simply restart the BMU and
turn the system back on with a charging source readily available to
start charging as soon as possible.
In rare cases, a dark start
procedure is required using an alternate source of DC to “jumpstart” the
BMU and keep the system on long enough to begin charging.
There
is little danger to the batteries or the BMU if it turns off and has to
be restarted normally after brief system outages. However a system that
shuts down and stays off without any charging for prolonged periods of
time may cause long term damage to the battery cells if a parasitic load
is allowed to draw down the voltage extremely low. Even in cases where
there is no damage to the batteries, it is understandably very
inconvenient if the power goes down and the system needs additional
efforts to get it started, much like allowing your vehicle to run out of
fuel on the side of the road.
Please note that battery cell temperature is an important factor, do not try to charge the system if you suspect the cells are frozen. Doing so may irreparably damage the modules and void the warranty.