This is certainly not a recommended safe practice.
Bolt the rectifier to a chunk of sheet aluminum to act as a heat sink. Make the connections to the battery pack. Hook together all the extension cords you can find and plug in the rectifier. See what the charge rate is in amps. If it is over 10 amps, borrow some more extension cords. (The extension cords lower the voltage.)
Mine turned out to be 2 amps. I kept removing cords. One short cord worked fine. 10 amps when the batteries were low tapering down to 5 when the batteries approached full.
I recommend that you have a timer that will shut off the power when you expect the battery pack will be fully charged. If you don't have a timer, set an alarm clock to remind you to turn it off. I use the alarm on my cell phone to remind me to check on them every couple hours. Remember, the max voltage you should charge to depends on temperature.
A ways back I explained how to use a transformer in buck or boost mode to give better output voltage control.
Please be careful. I am not recommending anyone do this. Electricity is dangerous. Touching bare wires and connections can cause shocks which can be fatal. Don't set your lawyers on me! You've been warned.