That is the trouble with these articles in the Professional Mags now, very short on Technical detail. Little more than "Advertorials".
However, you are saving on the purchase and running costs of one engine, as on most supply ships, 2 engines plus the battery can provide all the power required,(with the third engine on standby in case one of the others fail) to maintain position on DP and three engines would give full transit speed.
The newer type Diesel Electric plant where the engines run at variable RPM and generate constant Voltage DC power, distributed via Ring Main to the Inverters for each propulsion motor and the ships domestic supply would mean the battery could be charged from the DC ring main and discharge power back to it, without the need for Battery chargers and inverters to connect the Battery to the system (as would be required with an A/C Generation and distribution system).
Combine that with RIM Magnet propulsors and you have a modern efficient, low maintenance ship.
It is always better to ask a stupid question than to do a stupid thing.