Dell notebook battery at 58% capacity despite being advertised as new

I bought a Dell notebook on Refurbed, paying extra for a new battery. After a few days, since it wasn't holding charge well, I checked with a dedicated tool and found that the battery (despite showing 0 charge cycles) is at only 58% of its declared capacity. I contacted the seller to request a partial refund, but they refused and offered a full refund upon return of the notebook instead. I need the laptop for work and can't be without it; besides, the rest of the machine is in excellent condition and the price was good. Has anyone been in a similar situation? If I open a dispute with Refurbed, am I likely to get anything out of it?