Hi, I’m slightly confused, but any electronic needs a battery. After leaving a device uncharged for months can cause the battery to drain completely flat. When this happens, it is hard to charge it up again, so a new one is needed. In stall the new one. It may make the device work but everything needs to be connected up. If it doesn’t work then comment and we will see what else needs to be done.
Also, if you are not sure of how to replace the battery yourself, take it to a reputable repair shop and they will be able to install the new part fairly cheaply.