Slow performance after battery replacement

I recently replaced the battery on my 15" Mid 2012 RMBP. I'd installed a clean version of High Sierra before installing the battery. Since replacing the battery, the performance fo the Mac feels a but sluggish, glitchy almost.

Here's what I did:

Tried resetting the SMC - which didn't seem to even work properly. The light on the power cord didn't blink to indicate anything had happened.

Startup progress bar also seems to stall for a noticeable 5-10 seconds now, about 3/4 of the way through. Not a killer, but a noticeable difference.

Any thoughts are appreciated.

Thanks!