Glaxy SII not charging properly huge battery drain?

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http://androidforums.com – So I have this Galaxy SII. When it charges, the power tends to last about a day, which is fine, I can deal with that. However, it doesn't when I plug it into the charger, it doesn't register as charging and the battery seems to drain (liek form 68% to 32%). If I switch the phone off completely and then plug the cable in, it switches itself on, not to the usual off battery loading thing, but actually completely on, still not charging. Last night, I managed to get it to charge completely, after it had drained itself to 0%, by plugging it in while drained. It would do the battery symbol (General)