Why is the new battery not powering the device?

Why is the new battery not powering the device?
I received my new battery for my nest 2nd gen thermostat from I fix it. After I installed it, I charged it with a USB charger. After several hours of charging, the Nest device won’t turn on. When I plug it into the wall, I get a red blinking light at the top. I know I’m installing the battery correctly because, I was able to install the old one and get it to work. Is there a problem with the device or the battery? Thanks!

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