Question, the charger and the battery (the new ones) are they exact same models you had originally? OEM ones. Or are they aftermarket? If they are aftermarket, then knowing for certain what the problem is would not be possible. Alas, aftermarket ones can have problems and not work with a device, even if it was something that needed replacement. An example, some manufacturers put chips and other means of detection on their batteries, making aftermarket ones for the device useless.
The problem you describe sounds like a battery issue. That is what the 4 blinks normally means.