Not booting after battery replacement

Ideally one should try the new battery before installing it and if things aren’t as expected then try again the old one to rule out a faulty battery or possible other damages.

Alternatively, try disconnect the battery and plug-in the cable, with its original charger the Mac should be booting on its own and let you check if at least it still works somehow. If it doesn’t start at all or if it behaves the same with new and old battery, chances are that something went wrong during the repair and the logic board got damaged somehow.