Hi, I use a 12/24v battery charger with a potentiometer, which gives me a wide adjustment range from 1-40 amperes. This gives very high precision and control at work to avoid burning the car paint.
I use this from Amazon, works great C20 Adjustable Battery Charger 12V 24V 36V 48V, 12A Pulses of High-Voltage Battery Desulfator Maintainer with Smart Chip for Lead-Acid LiFePO4 Lithium Batteries BLB-C20