Default weird charge issue

hi folks, got a strange query id like some info on,

ive got a nexus 7 and its currently running a cyanogenmod build but it doesn seem to be charging properly as if i have screen on it will slowly discharge even though its plugged into the official 2amp mains charger. i dont remember this happening on the stock os, just wondering if it is normal or should i be looking at changing to a diff rom
Devices: Nexus 7 (Grouper) | B&N Nook HD+ | Dell Streak 5 | Motorola Milestone |
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