A really weird trick I learned passed on from a body shop instructor. Spray the terminals with Windex and wiping them. For whatever reason, it removes all the deposits on the terminals and they look like new. Don't mock it until you have tried it.

Be sure to coat the terminals with petroleum jelly to keep them from oxidizing. Then reattach the terminals.

***EDIT*** I know it is weird. But it works.

Pour coca cola on them. Let sit then wipe off. You can also buy a battery terminal brush. Coat with dialectic gel after cleaning.

use hot water with baking soda to clean the terminal, u can do it using a metal brush for better result. After cleaning, apply some grease on terminals, then reattach connectors.

A steel wire brush will clean battery terminals just fine. Side terminals was one of GMs dumbest engineering decisions with that teeny little soft bolt head they used.

Baking soda then after cleaning use Vaseline and a penny to prevent further problems. Some people use oil in place of the Vaseline.

There is actually a special tool for the job,

called a "battery post cleaner"

It has a cylindrical wire brush that is used for the post terminal,

and a tapered reamer to recut the cable terminals,

which are tapered if you haven't noticed.

Ebay it,

they come in at less than !0 bucks.

And last for ever,

well as a professional mechanic I have wore out 1 in decades.

So nearly for ever.

if the battery is under the bonet boiling water easily cleans it ...then dry terminals and vasaline them

Use a wire brush. Also clean the cables.

You have to remove the batt cables and clean the all the surfaces with a wire brush . That is how you do it.

Baking Soda and water then scrub with a brush.