[Al Skierkiewicz]

We have checked battery chargers here at work over many years and several battery technologies. If one just checks the charger connected to a battery, you will find a fairly steady voltage with little transients when the impedance of the connection is low and the battery is almost charged. (Remember that battery internal impedance varies with state of charge) However, the smart chargers are designed to sense battery delta voltage and will regularly switch from charge to sense. If there is any impedance in the line, there will be significant "noise" generated in high impedance paths as they exist. Lead/acid technologies generally perform "constant voltage" charging which by definition is not a low impedance path. The KOP chargers and most of what has been discussed, has #16 or #18 wire which compared to the battery adds significant impedance as well. The addition of a scope probe also grounds the circuit through the scope so that noise that is present may be removed by the method used in examining the noise. Differential scope methods should be used when examining this circuit.