[Q] Xperia Z hard to charge?

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http://forum.xda-developers.com – I'm running PAC rom not undervolted or anything and I realised it takes very long for the Xperia Z to charge itself. I went to take a nap at 4pm and woke up around 6.30, battery was 21% and I managed to only get it to 77% when I wake up. When I open Whatsapp or do some stuff on the phone while its charging, the battery percentage will go down instead of up. I'm using AC to charge and have tried the "Fast-Charge" mode on my motherboard which ups the current to 1.5A but the battery will still go down when charging. I'm not using the original Sony cable though, I'm using the one that ca (HowTos)