Black+Decker's Pivot Vac handhelds are popular for quick messes, cars, and stairs, but most models rely on an internal rechargeable battery that eventually loses capacity. If the battery is sealed or not cost-effective to replace, "replace" is the practical outcome once runtime drops dramatically or the unit won't hold a charge.
Before replacing, check easy wins: clogged filters can make the motor seem weak, and dirty charging contacts can prevent full charging. Repair is worthwhile when the issue is a replaceable filter, nozzle latch, or switch, and the battery still provides decent runtime.
Replace when suction is poor even after cleaning, when the motor is noisy or hot, or when the unit only runs briefly off the charger. Because handhelds are low-cost and heavily used, battery aging is usually the dominant factor in the repair-vs-replace decision.