Can you charge a spare PAPR battery while you're still working?
Yes. The pack is removable and charges either on the blower or off it, so a second battery can sit on charge while the first is on your belt. Whether you need one depends more on your airflow setting than your hours.
The pack is rechargeable lithium, 12.6 V, and it charges either way, on the unit or removed from it. That is the part worth knowing, because it means a spare needs no separate cradle and no second charger.
Whether you need a spare at all is a different question, and for most independent shops the answer is no. Documented runtime is 7 to 8 hours on the low setting, which covers a working day, and it charges overnight like everything else in the shop. A spare earns its money if you run on the highest airflow setting, which trades runtime for air, or if you work somewhere you cannot leave things on charge.
One thing to watch that is not about the battery at all: if runtime has gradually dropped, look at the filter first. A loading filter makes the blower work harder for the same airflow, and that shows up as shorter battery life long before it shows up as anything you can feel.
A spare battery is $65 if you decide you want one.
Related questions
I have a beard and I wear glasses. Is there anything that works? Do I actually need a respirator for woodworking, or is that overkill? Does the carbon pre-filter mean it handles fumes? Should I spend on dust collection or a respirator first?The Breathie Thingy
A powered air-purifying respirator for woodworkers. $499 for the first 30 units of each batch, including a spare filter kit.
See the current batch