This is normal; the Mk2 will continue running down to an input power of about 6v. As the power input dips below 10.16v, the empeg assumes it's losing power and saves the current state in flash, turning the display off (which also turns the amps off).

It them sets a timer; if this timeout is reached, power obviously hasn't gone away and it turns the display back on and continues. The battery symbol indicates that the empeg is currently ignoring any more power fluctuations - we added this as one mk1 customer had big amps and a weak battery leading to this situation:

empeg turns on amps. Power drops below 10v, display & amps off.
Power recovers, empeg turns amps back on. Repeat.

Hugo