I use the charger for 4 pcs Panasonic NCR18650B_2PCM 18650 Li-ion battery (3400mAh, protected design). The entire automatic process (check, discharging, charging) takes on two charging cycles, which ran so far, around 8 hours, during which device and battery heated strongly in the last few hours to full charge. I can not judge whether emanating more from the device or from the battery. The heating is accompanied by the typical hard-plastic exhalations which hopefully subside in future charge cycles. So soon I load only in the basement / workshop / chamber, as far as ventilated, but not in the living area. As a result, the device does what it should, if I attach it to the subsequent service life of the batteries in a FENIX spotlight.