Congratulations on your new KIA Soul EV techrider!
I've been driving mine since May 2019 and love it. In Vancouver climate I have not seen battery heater kicked in even once - it would show in the energy consumption screen. Maybe it's not cold enough? Or maybe because car lives in the heated garage? IMHO the "Winter Mode" only use battery heater when needed, so no harm in having it enabled when it's warmer outside.
"When a dedicated 2 kW battery heater is available (as in the Canadian version), it is used primarily at sub-zero temperatures (0C or 32F) or when the driver enables an optional “Winter Mode”. The battery heater, if present, is located outside the battery pack and warms the liquid “coolant” just before it enters into the pack.
The winter mode uses extra energy to warm the battery pack to allow for full regenerative braking and quicker fast DC charging. Colder pack temperatures force the battery management system to restrict the amount of power that can recharge the battery in order to avoid damaging the carbon graphite anode. This is an issue common to most lithium ion batteries. Cold temperatures are not much of an issue for power coming out of the battery except under rare and extreme conditions like down near -40 degrees."
More info here: https://electricrevs.com/2018/12/20/exclusive-details-on-hyundais-new-battery-thermal-management-design/
12 V Aux. Battery Saver+ feature won't do any harm either. I have it enabled.
"Battery Discharge Warning" alerts are normal. When car is started, main battery recharges 12V battery, but when ignition is off 12V battery powers all the electronics and loosing charge. If you want to use Audio or heater with ignition turned off - use Utility mode.