Battery indicators on disposables are usually pretty basic. You'll often see a single LED that lights up when you inhale. It might be green when fully charged, yellow when it's about half, and red when it's low. Some devices blink when the battery is critically low.

But here's the thing: these indicators are not precise. They're more like a traffic light than a fuel gauge. They tell you the general state, not the exact percentage. So if your light is yellow, you know you're past halfway, but you don't know if you have 40% or 20% left.

If your device is rechargeable, you can usually charge it when the light turns red. If it's not rechargeable, the red light means it's time to get a new one.