Sand/Shot/Bead-Blasting

I'd be inclined to say sand. Really important not to get it in the wrong places, of course, and to clean up afterwards.

Pop it in a dishwasher.

Another possibility is electrolysis.

Take a look at:

It may go straight in or may display a screen about not being logged in, but there is a "click HERE" bit to continue without.

SteveW

It's not going to work with any modern battery charger. They detect battery voltage and won't switch on if it's below ~10V. Utterly useless for charging a flat battery. Which is when people get the battery charger out.

Old computer or CB radio PSU. Or a 12v transformer and rectifier.

Don't use stainless anode. The chrome from stainless will be consumed to form a yellow chromate solution in the electrolyte. It's poisonous and carcinogenic. You can't dispose of it, it's illegal to pour it down a drain. It will poison the biology of the waste treatment plant.

Are you quite sure? This just makes no sense at all.

Correct. On those rare occasions when I need to charge a battery I just make up a charger from a suitable tranny and full wave rectifier run off a variac.

I thought it was just me :-)

Many chargers are voltage sensing. They can detect reverse polarity and sometimes a 6V battery.

If it doesn't 'see' a 12V battery it will assume it isn't and won't turn on.

It saves damaging the charger at the expense of not charging a truly flat battery. Fewer expensive customer returns from idiots.

There is usually a relay, the coil of which is controlled, via a diode, by the battery, which then connects the charger to the battery. To prevent damage by reverse connection. Which also means it won't even attempt to charge a totally flat battery. Common feature on most battery chargers for about 30 years.

He's right about modern, smart chargers. They are great for keeping a rarely used car charged as they automatically switch to trickle mode and can be left indefinitely, but they detect unusually low battery voltages as faults and refuse to charge.

I keep an old-fashioned, dumb charger in case I need to start such a battery off. Usually, 10 minutes or so is enough and then you can switch to the smart charger and foget about it for the night.

SteveW

Thing is most older chargers have no protection against wrong polarity connection, except perhaps a fuse. Which you won't have a spare for anywhere. ;-)

OK I can perhaps see the case for electrolytic cleaning (followed by two pack epoxy) on a classic that the OP is planning to show, but isn't that actually a bit OTT in most cases?

It is simple and cheap, requiring no equipment other than that that many people will have at home or could obtain cheaply though.

SteveW

I was very surprised at how well placing rusty things in ordinary vinegar works, left for a day or so, all the rust has fallen off. Cheap, safe, excellent method.