Proper way to check a battery
The better way to check battery capacity is to use specialized device like MH-C777PLUS to measure real battery capacity
I recently bought 2900mA battery on eBay, and it does have more juice in it. Here are my measurements so far using MH-C777PLUS:
Stock (2500mA) battery capacity when measured on MH-C777PLUS device: approx. 2400mA
The 2900mA battery: approx 2700mA. So while it's a little further from the claimed capacity compared to the stock battery it does have 12.5% more energy than the stock battery.
I also ordered 3000mA Gold battery from eBay but didn't receive it yet. Will post test results as soon as I get it.
I was trying to post links to the MH-C777PLUS and both batteries but forum rules won't let me post links yet