The only way I've seen to find self-charging gear in Heat Signature is to hope that a "liberator" character eventually shows up with something. Is there a way normal characters can find self-charging gear? There are various personal missions that are all but impossible without that kind of kit, but I haven't found any in all my travels (and I feel like I'm pretty late-game).
They're still rare, but my strategy has been spending all my money on "Overpriced Mystery Crate" from the Miscellaneous Shop (and the Liberation Mission eventually).
I've unlocked a few of those items for sale; but overpriced mystery crate is always there.
Basically I just spend all my money on the cases and then sell all the junk and keep anything better than current inventory.