The benefits of a portable generator include that they have a low upfront cost and are portable. The drawbacks of a portable generator include buying and transporting fuel, they are loud, high in emission, require maintenance and are not on standby.
The benefits of a battery include that they are silent, emit no fuel, enable you to store and use your solar PV energy, are on standby and have incentives available through Energy Storage Solutions. The drawbacks of a battery include that they have a high upfront cost, require professional installation, interconnection and permitting, and are not portable.