Is a 9v battery adequate for node MCU + motor shield + 2wd .

I’d say not - very underpowered are those 9v batteries.

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9 Volt 500 total mAh 15 typical draw mAh

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It rather depends on what type of 9v battery you’re talking about, and what you’re using it for.
I assume that 2wd means s9me sort of two wheel drive system for a vehicle?
If so then a great deal will depend on the type of motors you’re using, the gearing ratio that you’re using, and the sort of speed and distance that you’re hoping for the device to travel.

Voltage in itself has very little to do with the equation, what’s more important is the capacity of the battery in Amp Hours.