You'd be surprised how many vapes have a tiny LED that blinks red when it's dying, but no way to tell how much charge is left. That's frustrating and unsafe—you might drain the battery completely, which stresses the cell.

Look for a device with at least a three-stage indicator (green, yellow, red). Some, like the VERTEX-25K, have a small percentage display. If you're always at 1% without warning, that's a bad sign.

A good indicator helps you charge at 20–30% rather than 0%, which extends battery life and reduces the risk of over-discharge.