Corrosion on copper contacts

Could be any of those.
Could also be the wiring,
the connectors,
or it could be the fuse.?

If you don't know what you're doing take it to the shop or an auto-electrician.
That what these things were invented for.?

You can take the bad batteries out and clean up the battery compartment, using isopropal alcohol (rubbing alcohol and a lot of q tips). . Problem is if the acid wrecked the contacts. Light corrosion (green,corroded copper color) needs to be removed with sand paper or emery cloth, until all the contacts are shinny metal again. maybe spray some silicon on the newly shinned metal to slow down re-corrosion. If the damage is serious, i.e. the metal is eaten away, then someone with soldering experience needs to desolder the bad metal and resolder in good. This can be quite expensive is you take it to a technician.

Yes, you can replace the cable end.

Check the electrical spring connectors at the door, and the contacts at the door pillar. They are notorious for corrosion. Take some steel wool or very fine sand paper, rub against the contact areas until a copper color returns. The pillar contacts get corrosion and very poor continuity thru the connector. The spring contacts in the door can also get corrosion on the back side at the connector, try cleaning them on the outside first before attempting to remove door panel.

Older printers can do funny things. It is probable that the little copper contacts on the ink cartridge are not making good contact with the printer which is giving bad information to the computer that the ink cartridge is empty. A two year old printer may have some corrosion on the printer's contacts. Remove the ink cartridge and use a soft pencil eraser to clean the printer's contacts.

I am assuming that you mean with the electric door lock and not the key. If the lock works with the key but not the electric, do the following. Open the rear door and find the electric contacts. (one side will have 4 spring load prongs and the door side will have a flat plate with brass/copper contact plates) Take a small knife or sandpaper and scratch off corrosion on the prongs and the plates. Once they are clean and shiny, the electric locks should work.

Use a pink eraser like that on the end of a pencil. In fact, use a pencil.
Perry

If you are sure the battery is charged, the battery may not be making a good contact with the copper connections. Make sure the contact surfaces are clean and have no corrosion. I have a phone that has this problem occasionally.