If you're using the Argos drill batteries and motors, would recommend just running a single battery to start with until you're happy with the wiring before thinking about adding a second battery in parallel or series.
Whilst the Feathertwo can handle running 2 batteries in series for a combined 24V, doing so will be overvolting the motors and pushing the Ampage limits of the esc which is not a great thing to try if it's first build territory, just adds a ton of extra things to go wrong.
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