Yeah ^^.
When the battery is freshly charged and has a relatively high voltage, the PWM pauses longer between the on stages. As the voltage drops, the pauses get shorter. All this to keep the output voltage to a more or less equal value during the lifetime of the charge (which could, for example, run from 4.2 volt at the beginning to something like 3.2 toward the end). A PWM battery is regulated, which means the output voltage is always equal, independent from the actual voltage charge. This results in a more consistent
vape.
At least, that's how I understand it.