Battery Indicates Plugged In & Charging But Percentage Never Increases

Hi,

I have an iPhone 4 in for repair that won't charge. When it's plugged in I get the chime to say it's plugged in and also get the charging indicator to say it's charging. Unfortunately the battery percentage never increases.

I've tried replacing known good docking port assembly and known good batteries but get exactly the same issue.

Leads me to believe there's a component on the board that's not playing ball but my question is what?

Any ideas would be greatly appreciated!