Problem with battery after switching to SSD drive

HI

(macbook pro late 2011 13 inch, 2.7 Mhz, 8 Giga ram OS Yosemite)

I have replaced my hard drive to a new SSD drive (Samsung 850EVO 500 GB).

Before that my battery worked wonderfully- when fully charged I could work normally (Wifi and "normal" use) for 4-6 hours.

Immediately after replacing I can "squeeze" at most only 3-4 hours of working.

Any one has encountered similar problem? what did I do wrong? I must say I did this upgrade for my brother's computer, exactly the same computer and he has the same problem but even worst.

(I ran a test with iStat pro and got "85% health battery").

Thanks for the help!

Dror