[franga2000]

They definitely don't make any sense for home battery storage, but the vast majority of even electrical engineers couldn't build something as reliably portable as these things. We used one of the bigger ones on a film shoot to power pretty much everything but the camera out in the field (literally in a field) and I wouldn't have even considered a DIY option. Even something as simple as weathersealing is surprisingly hard to get right and I doubt most even experienced electrical engineers could achieve these absurdly fast charging rates safely.