Identity component of Banach-algebra invertibles ($G_0(A)=⟨e^a:a\in A⟩$)

Finite products of Banach algebra exponentials form a subgroup: inverses are $e^{-a}$ and conjugation sends $e^a$ to $e^{ga{g}^{-1}}$. Each product is joined to the identity by $t\mapsto \prod e^{t{a}_i}$. The logarithm of an element near the identity puts a norm neighborhood of $1$ in this subgroup, so its cosets are open and its complement is open. It is therefore exactly the identity component of a topological group, and is an open, closed, normal subgroup. A product of exponentials need not be a single exponential in a noncommutative algebra.