Hi,
Appears as though the battery is failing and needs to be replaced. Even rechargeable batteries have a life span.
[https://www.amazon.com/HQRP-Battery-RCT6973W43-Voyager-Replacement/dp/B07BZNX1W6|Replacement batteries] (example only to show cost) are available online. Just search for ''RCA Voyager III battery'' to find suppliers that suit you.
Unfortunately I couldn’t find any good teardown or battery replacement videos or guides to help. There is [https://www.youtube.com/watch?v=d5wVhv0JjuM|this] which shows how to replace the screen. I realize that this is not the problem but it may help as it shows how to open the tablet etc, so access to the battery is possible. I admit that it is not very good though.
If doing this yourself seems too daunting, contact a reputable, professional mobile phone or electronics repair service and ask for a quote.