First the batteries need to be fully charged to an acceptance @ 14.2V - 14.4V of less than approx 1% Ah capacity at the 20 hour rate. At that point you can drive them to 15.5V to 16V depending upon the brand and TEMP COMPENSATED. If you don't have an accurate means to test before/after the time needed will be a crap shoot.

PLEASE DO NOT use a cheap charger for this. The current needs to remain low and the voltage high. Cheap chargers can become pretty unstable. A 5A bench top DC switch mode power supply is a great tool to use for equalizing. They allow full control over voltage and current. Mastech makes some pretty affordable bench top switch mode power supplies. I MUCH prefer them to "battery chargers" when doing equalization/conditioning charging.