This.
Although it could be that the battery is simply too weak. If you can get your hands on a battery tester Amazon, test it first.
Post back and let us know your findings. Best of luck.
Edit: Link
You can get a battery/alternator tester quite cheaply and figure out whether it's the alternator. Example below, but any auto parts store should have them.
https://www.amazon.com/CARTMAN-12V-Battery-Alternator-Tester/dp/B00EXIEVO6/
This is what sparked my question. How would this work?