Power efficiency = REAL power in/REAL power out X 100%
1.) Starting of with a flat battery, measure the battery voltage and charging current every hour and real power in. Calculate efficiency at every hour, plot efficiency v. time .
2.) Load the unit to 100%, measure Pin and Pout calculate efficiency, repeat with load set to 90%, 80%. . .
For trickle charge, remove the load, leave on charge until the charger goes into trickle charge, measure Pin and Vbatt X I batt (Pout?)
"current should be in the millivolts ", current should be in milli AMPS. Trickle charging is when the charging current is just enough to offset the chemical degradation of the battery, so very low.
3.) Efficiency of battery, I guess is the ratio Pin/Pout. The problem is that you don't know how much power there is left in the battery. batteries should not be run flat but run down to some threshold voltage set by the battery manufacturers (who will know their storage efficiency). So flatten a battery down to its minimum voltage, measure Pin and battery V and I, every hour until battery charged. Put battery on load , measure V and I every hour until V is down to minimum voltage. calculate the total Pin and Pout. Work out efficiency as tot Pin/ Tot Pout.
Frank