[smaddox]

Building/refurbishing lead acid batteries wouldn't be all that difficult immediately post collapse.

Solar panels can also be refurbished. For poly silicon cells, it's mostly the contacts that degrade, and you can improve that with a soldering iron. A bit more work, but still doable, would be a forming gas anneal, which can additionally passivate defects.

[NegativeLatency]

I suspect you could scrounge materials for a nickel iron battery without too much trouble.