In reference to the TPS2000 + what do you mean by "hot-swappable" batteries?

In reference to the TPS2000 + what do you mean by "hot-swappable" batteries?

While the product is running on one battery, you can install another fully charged battery without having to turn off the oscilloscope or interrupt normal operation. (The oscilloscope drains only one battery at a time and the lowest-capacity battery first.) With the optional TPSCHG external battery charger and optional 3rd battery, hotswapping can provide virtually unlimited operating life.