battery discharging while on charger?

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http://forum.xda-developers.com – I noticed while playing MC3, [Paranoid Android rom] my battery percentage would slowly drop. I was plugged into the stock charger, but I was using a 3rd party [longer] micro USB cable. I plugged in the stock asus micro USB, and I thought it started charging again. what's up with this? just a cheap cable? it's always worked fine in the past.. today I was playing again with the non-asus cable, and it was slowly going down [from 99% to 97%], and I plugged the asus cable in again, and used a USB 3.0 extension, and it went down to 96%. All of this time, the charging icon was there. So I (HowTos)