You don't necessarily need to have structural battery to be firmly attached to something, nor have it to be housed in some inaccessible compartment. At least,

You don't necessarily need to have structural battery to be firmly attached to something, nor have it to be housed in some inaccessible compartment. At least, the battery case can support its own weight. This alone can shave up to 100kg from the battery, and make the whole task of engineering it that much easier. This is what all that "blade battery" things is about. Another idea is that if your battery chemistry is not prone to bursting in flames like gasoline, the battery can become a decent crash energy absorber. This way instead of having to add weight to protect the battery, you can use the battery instead to reduce the weight of existing crash protection structures.