DIAGNOSIS Battery capacity has degraded. This is normal wear and tear for lithium-ion batteries, especially if you frequently run it down to zero or store it fully discharged. It can also happen faster if the filter is clogged, making the motor work harder and drain the battery quicker.
FIX First, rule out a workload issue. Clean the filter (rinse with cold water, dry 24 hours) and clear any clogs. If runtime is still short, you need to condition the battery. Run the vacuum on MAX mode until it shuts off. Then, charge it fully and uninterrupted for the full 3.5+ hours. Do this 2-3 times. This can sometimes recalibrate the battery’s internal gauge and recover a bit of performance.
IF THAT DIDN’T WORK The battery pack itself is likely at the end of its life. For the V8, the battery is a user-replaceable unit. You can order a genuine replacement battery and swap it yourself—it clicks on and off the back of the main body. No tools needed.
HEADS UP Using MAX mode constantly will drastically shorten both your runtime per charge and the overall lifespan of the battery. Use it only for tough spots. For maintenance, regular mode is plenty.