voltage fluctuations
A 3 stage charger has 3 voltage settings for the 3 stages. 1 Bulk charge, 14.4 volts.2 Absorption charge, once the battery voltage wants to go above 14.4 volts, the charger will decrease current to the battery to maintain it at 14.4 volts.3 float charge, once the absorption charge is complete the charger will maintain the voltage at about 13.3 to 13.6 depending on the charger. This setting keeps the battery from self discharging.Your 15.23 voltage is an equilization charge voltage. Are you reading this voltage when the charger is on and in the "recondition" setting? If so this is a good thing. Batteries should be equilized about once every 4-6 weeks. Water the batteries with distilled water, and bring them up to this voltage and leave the charger on for 1-2 hours. The batteries will be bubbling vigorously. without monitoring charging amps it's hard to say exactly how long to equilize. after charging let the battery sit with no load or charge for 3 hours. A fully charged battery will read 12.6 volts. plus or minus .1 volts. You need to realise that voltage will fluctuate a bunch depending on load, state of charge, and condition and type of battery.