Originally Posted by thiel
I always thought that multistage chargers started high like 18 and then stepped down to a 12v
float charge as the batteries got full. (I thought that was actually the very definition of a multistage charger.)
Battery charger descriptions have changed over the years. What we now call a staged controller: (... and once described differently)
1) Sarts out in a current limited mode. It shoves X amps in and watches the voltage.
2) Levels out as some defined voltage and sits there for a while
3) Cuts back to a lower voltage and "floats" there for a long time
4) Maybe (if it's a 4 stage) pops up to a higher voltage for a brief time to stir things up.
Normal voltages are all in the 13 to 15 V range for typical lead acid batteries at 70F. They shift by > 1/2V up or down at typical 3 season camping temperatures.
In the opinion of a lot of people 18 to 20 V on a battery is simply insane. When you talk to the guys who make those chargers, their answer is that it's intended for use on batteries that already are severely compromised. The main point is that you don't want to grab just any charger and slap it on your RV batteries. You need to get one that is designed for your application.
Why not name names? Most outfits make a bunch of chargers. They also change what they do over the years. What they made two years ago may not be what they are selling today. Model A may not work like model B. Being *sure* that this one is a problem is just as hard as being sure that another one is ok.