The Evolution and External Power
The Evolution mount can be run from external power if the internal battery is low or completely depleted. But, the mount sometimes requires more than 2 amps in surges (for example, when starting a full speed slew), especially if you have the StarSense camera attached. If you also have the SkySync GPS module attached, it will definitely need more than 2 amps.
The power adapter Celestron supplies with the Evolution is just 2 amp. If you are running with external power attached and a surge requires more than the external power can provide, the mount will try to supplement with the internal battery. If the combination of external power and internal battery are insufficient, the hand control will most likely reset and you will have to realign.
Lead acid gel-cell batteries can easily provide more than 2 amps. Some lithium batteries can and some can't - refer to the specifications of the battery. This article discusses various external power source issues.
Finally, the mount has a setting accessible via the menu (Peripherals ->
Power -> Supply) which sets the maximum current the mount will attempt to draw
from external power. The default is 2 amps. If you set it higher to overcome
resets due to surges and then later use the Celestron-provided AC power adapter,
the adapter could overheat and be damaged. You should always set this
to the actual power capacity of the external source or lower, NEVER HIGHER.