It measures batteries of 1.5V with exceptional accuracy and with minimal deviation downwards (e.g. 9.20 instead of 9.35) for 9V batteries. The comparison is always made with a regular multimeter.
Unfortunately, it cannot measure, not even approximately, 3V lithium (button) batteries. (I thought it would do so because it resembles the corresponding Varta).
Otherwise, it gives the same indications as the cheaper BT-168D models that work without a battery. However, it excels in size (clearly smaller)