OK, I read the book, such as it is, and I now understand that a Charge Efficiency Factor is the ratio of Amp-hours required to charge to actual Amp-hours charged. Or stated another way, a CEF of 90 (the default CEF in the Link 10) means that after a discharge I have to recharge 100 Amp-hours for every 90 Amp-hours actually pushed into the batteries. I am uncertain if what is displayed on the Link 10 is the actual AHs in the battery or the theoretical CEF AHs - probably actual. Anyway, left to its own devices, the Link 10 recalculates the CEF after a certain level of discharge and based upon some user-entered values, like "battery charger finish voltage." I took that to be the 13.4 volts my True Charger 40 floats at. Anyway, the Link recalc'd the CEF to 92, which means to me that now I my batteries are getting 92 AH for every 100 AH charged, or a bit better than the default. That seems OK for six year-old lightly used batteries. Still playin' around with this... Rich Gano Calypso (GB42 Hull # 295) Panama City area, FL