The BT-79Q Rechargeable Battery for Topcon RL-H5 Series Rotary Laser is an effective power source that works with Topcon’s RL-H5A and RL-H5B Rotary lasers. The BT-79Q battery is an NiMH rechargeable battery type that can operate up to 60 hours which is great for a whole day use. In addition, it offers a 4.8 DC voltage (VDC) and a 7,000 milliamp Hours (mAh).