Be aware that auto batteries can be explosive due to flammable gas in their vicinity, so to minimize sparks and keep your face away from a battery when doing work on them is advised. I would recommend to plug the charger into the wall power after the + and - are attached. Explosions are rare, but they do happen. Just sayin'
A battery charger will show a higher value on it's gauge when first put into charge mode, then fall lower as the battery is charged. For example, a fully dead battery will pin the charger gauge needle all the way to the right which is showing you that the charger is putting out full power to charge the battery.
Cleaning the terminals requires removal of the cables from the battery, and clean all contact points. Go easy when removing the cables so you don't break the battery terminal down inside the battery. Note too that terminals that fasten to the battery cables with bolt type clamps are often dirty as well. Even though they are frequently used, it's not a matter of if they will fail, it's more likely when they will fail, but cleaning them is not impossible. A stiff wire brush is good to clean the cable side of these types of clamp terminals. If the cable corrosion is extensive, I would go so far as to cut off the corroded section, if cable length allows. If you are near Buffalo, magnesium chloride is likely in use as a road treatment. Mag chloride makes road salt look like baby food when it comes to comparing corrosive materials. Very nasty stuff. Salt does not melt ice well at below 20 F, and so Mag Chloride is used to enhance the salt's melting capabilities. Those who follow vehicles closely when Winter roads are wet usually get plenty of salt and Mag Chloride under the hood and into the radiator and AC condenser.
If you have access to a digital voltmeter, here is how to test your battery:
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carbatteryonline.net/car ··· ter.htmlTake note of when and how to check and temperature issues.
Alternator check
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easyautodiagnostics.com/ ··· rnator-1
