One experimenter discovered that scrubbing them with the edge of a stiff business card helped to make
|with (nonCanon this time) charger contacts|
Parts: squeeze-bottle of cleaner (I use a citrus-based cleaner from PlanetArk, which seems to be able to clean almost anything off without being excessively invasive); spray-can
Lightly spray WD-40 onto contacts. Gently but vigorously rub along the contacts with toothbrush. Paper-dry the contacts.
|wider view of brush on contacts|
(optional) When thoroughly dry, add a touch of light machine oil. This wards off moisture.
This appears to be just as effective with 3rd-party battery packs.