Fan goes to high speeds with 4 Safari tabs and battery discharges?

Hello,

I recently replaced an almost exploded battery on this MacBook Pro 13" Early 2011 and replaced the HDD with an SSD as well. It's currently running Sierra 10.12.6.

Lets say I'm fully charged at 100% and I'm on battery power. The fans are quiet when I boot up the computer, but as soon as I open 3+ tabs on Safari simultaneously or do any strenuous task (doesn't matter what I'm doing, YouTube, web browsing, whatever) the fan goes berserk and the battery goes from 95% to 2% within 2 seconds no matter what. I can use the computer at 2% for a while if I close the tabs and the fans return to normal (feels like more than what 2% should allow me to use). I can use the computer with a charger while the fan is running at max speed, but that's getting annoying as well.

Has anyone experienced a similar problem or have any idea what is wrong with this computer? I am not suspecting it's the aftermarket battery's problem as it wouldn't necessarily cause the fans to run at max speeds. I don't feel any heat coming from the battery side either.

Thanks for your time.

-Jm