Gary...going by photos and search Sears....I believe this link is what you have.http://www.sears.com/shc/s/p_10153_12605_02871234000P?vName=Automotive&cName=Batteries+%26+Chargers&sName=Battery+Chargers+%26+Boosters
This is Microprocessor-Controlled Battery Charger with Tester and GFCI Outlets.
Engine starts at 275amps for 12v and 125 amps for 6volts provides emergency starting power.
It said 60 amps rapid charge and 20amps fast charge and 2 amps slow/Maintenance charge.
It a good charger. However because of several batteries in parallel will require longer time to recharge due to low output.
Rapid 60 ampere setting is better...BUT it going to take allots longer charging then with 1 battery. Which mean the charger is going to get very warm or too hot but if you keep your checking power cord & plug to not get too hot or smelling rubber cooking. Use your IR gun on charger's transformer. Never go over 280° F. If so let it cool and restart.
Fast charge 20 will be safe setting but it is along time to bring it up. It depend what is batteries state of charge is will determine how long to bring it up.
Bottom line is that you will not heat bank of batteries as fast as you can with one unit. Again IR gun check it...never let it get over 125° F. to get max life.
Also 20 amps charging rate is dividing by the number of batteries...which mean slow still charging batteries.
I e-mail to Sears about model #71234 manual. They are having problem in their website for not able to download manual.
Sojourn for Christ, Jerry