I always ask my son about these things, they're a two-Tesla family.  But I notice, also from those instructions, "For property of a character not subject to an allowance for depreciation placed in service at your main home (personal use property), the credit for all property placed in service at your main home is generally the smaller of 30% of the property’s cost or $1,000."

So if the choice is between a generator or a small battery, both for $3,000, why not choose the battery and get the tax credit?  But then, as long as you're buying a battery for the car, why not buy a bigger one that will supply the entire house when an arctic freeze comes south and turns off power all across the state for days on end?  At least keeping the garage heated, will keep the vehicle from losing its charge.