Hello, Jessy -
The rechargeable battery for your Nextbook probably needs to be replaced. Eventually all rechargeable batteries need to be replaced.
Make sure you order or purchase in a bricks and mortar store the right battery for your Nextbook.
I don't know what model of Nextbook you own, but these instructions may prove helpful to you:
https://www.ifixit.com/Guide/Nextbook+8+Battery+Replacement/39351
If you do not feel comfortable in following the steps provided in the link above, find a reputable computer repair business near you, take your Nextbook there, and ask a technician there to open the Nextbook, determine what battery is needed for replacement, order the battery, and install it. Note: You will probably be provided an estimate of the cost of the work and will probably need to pay an initial fee which will be deducted from the final cost of the battery and the technician's work.
Best wishes.