I have a Ultrax and Powerextra battery. The Ultrax IR readings are cell 1- 6mohm cell 2-2mohm cell 3-2mohm cell 4-7mohm. The Powerextra battery readings are cell 1-8mohm cell 2-2mohm cell 3-2mohm cell 4-6mohm. Does anyone know why cells 1 and 4 are always higher in IR readings than cells 2 and 3?