Hi,
''If it is not holding a charge'' then perhaps the battery is failing and needs to be replaced. Even rechargeable batteries have a lifespan.
Search online for [https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2499334.m570.l1313&_nkw=btr6700&_sacat=20357|BTR6700 battery] (supplier examples only) to find suppliers that suit you best.
Here’s the Ifixit [guide|15204] guide that shows how to replace the battery in the phone.