MBP won't boot. Battery, charger, and magsafe port replaced. What do?

Wondering if I can get some suggestions with how to proceed with my current 13" 2014 MacBook Pro situation.

Earlier this summer I replaced the battery in my system from one I bought off a Canadian eBay seller.

It was working fine up until a little over a week ago when one morning it just wouldn't turn on. No light on the magsafe charger when it was plugged in, nothing. The charger was replaced about the same time with a brand new one, but I still tried it with a friend's charger but still nothing.

I tried plugging the old battery in without fully removing the new battery and that didn't work. I tried replacing the magsafe port on it and that didn't do anything either.

I had checked the battery connections with a multi-meter and I was getting some voltage readings, but I don't know if they are any good or not.

I'm past the 30 day return window for the battery, but I can do a free exchange for a new one. However, if the old one didn't change anything will a new one be any better?

Basically, I don't really know how to proceed here. The certified Apple repair place in my city originally quoted me ~$700 to replace the battery since they'd replace the whole top body. Is there another part I haven't thought of that I should look into replacing first?

I'm in a city with an Apple Store for the next week, should I take it there and have them run a diagnostic on it? Will they be OK looking at it if I replaced a bunch of the parts myself?

Thanks!