Replaced mid 2012 Unibody MBP 13” battery-shutting down

I’ve seen similar issues but not this one. I bought an iFixit battery replacement for my mid 2012 unibody non-retina MacBook Pro. I calibrated it according to the instructions. Everything is fine when plugged in but when I leave it unplugged and in sleep mode (Catalina installed), it will eventually just shut down. On boot up, it still shows 95% or whatever high percentage charge remaining.

The troublesome part is that on boot up, a good 50% of the time, it will start booting, then restart booting a few seconds into the boot.

One minor issue is that the size of the battery itself is just a little too large for the compartment—it was hard to seat it correctly and the bottom panel is now ever so slightly uneven.

I’m NOT having the issue of instant shutdown at 20% that some people describe. It just shuts down instead of continuing to sleep.

On startup, it will display the “shut down because of a problem” message. But I don’t think the issue is software since the only thing I changed was the battery.