BG1's algorithms is the simple technology in all three ways. It is mornitoring the battery terminal voltage and comparing measured value with build-in fixed voltage-capacity table then give a result of relative remain capacity status. For different chemical battery type, the voltage-capacity curve is different. Further, even for a same battery pack, this curve will be different at higher or lower discharging current. So it is easy to understand why this method only get a gross or rough result. Generally, BG1 has 10%~20% relative remain capacity tolerance.