The cheapest grid battery might be one that already had a life in a car. US20230387684A1, published by B2U Storage Solutions on November 30, 2023, describes operating battery energy storage in a power grid — and B2U's whole premise is doing that with second-life EV packs.
The CPC tags are grid-storage standard: H02J 3/32 (battery use in networks), H02J 3/381 (renewable integration), H02J 3/003/004 (network power adjustment), with G06Q 50/06 (energy markets) bolted on. Nothing in the classification screams "used batteries" — the novelty, if it holds, is in the operational management those tags enable.
Here is the grid mapping. Second-life packs are heterogeneous: different chemistries, different states of health, different remaining capacity. Running them together on the grid is harder than running a uniform new-battery system, because the control system must manage cells that age and behave differently. The IP value is in the dispatch and management logic that makes a mixed, degraded fleet behave as a reliable grid asset.
What this is not: a granted patent (it is a publication), and not a claim on second-life storage as a category. The filing stakes B2U's operational method. The economics — buying retired EV batteries at a discount to new cells — are the business case; the patent is the technical scaffolding that lets the business case work at grid scale.
From patent to grid, this sits at a genuinely interesting seam. The grid-storage deployment story is usually about new lithium cells and their cost curve. Second-life storage is a parallel supply that depends entirely on management software being good enough to tame degraded packs. B2U's 2023 filing is an artifact of that bet — that the bottleneck is control, not chemistry.