I have a schumaker, diehard automatic and a 2amp diahard manual. They behave strangely, maybe it's my fault. Charge over the clamps (even if wire brushed) can result in the green charge light never going on to indicate fully charged. Sometimes just moving the clamp - has the green light go on. So maybe std procedure is to polish the battery post, and not charge on the clamps. I do that. Regardless, it's hard to tell who has the best circuitry in their chargers and who is just hype. Any E engineers here who know the details? I have one battery that is 15 years old and still starts my audi. The buzz on that battery is that is must have a crack near the post as it turns the clamp green in a week. So i might have to replace it, over last summer it corroded the batter ground clamp until it crumbled. With 7 cars, I put time into battery care. Time for a primo charger (under 10amp of course).