There are a few possible issues, but they should all be easy to fix if it is the case. First, it may just be the charging cable. Cheap, third party, gas station chargers are not very good, nor apple MFI certified cables, meaning they can possibly damage your phone or throw its battery cycles out of whack. If that is not the issue, the repair place you took it to could have broken the charging port by accident. This would hold them reliable, but it is a fairly rare occurrence. Lastly, it may just be the battery not wanting to charge. This would also be the repair places fault, but it is not likely.
Of course, such a substitution is possible. Real specialists can replace the battery of any device with a new one. There are cases where replacing the battery will cause the device to malfunction in the future. In such cases, you can rely only on the warranty check provided to you by the service center after the replacement. I believe that replacing the battery gives your device a new lease of life. Of course, if all other features work well. If you need to replace the battery on your LG phone, consult first with employees who specialize in working with this particular brand. You can also get an lg v20 battery buying guide. I think that replacing the battery in this phone model will only benefit it.