iPhone wont start after changing to new battery

Hi,

I got a new battery and Iphone 6 plus screen from Ifixit. I did everything as explained and everything went well. Since its a new battery, on powering on it ask me to connect to a charger but on connecting to one, it doesnt charge. When I connect the charger, a large battery comes up on the screen with some red level indicating low battery but I don't see the lighting sign next to the battery . I kept the phone connected to the charger for an hour still it did not power on. Can anyone please help me with this?

Thanks,

Chintan