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Originally Posted by dkoldman

So out comes my old reliable Battery Charger. See picture. I will have to use it on the 50 amp setting to see if the unit works. I am going to trust the ACE versus going with my instinct. I can always stop it if it gets too hot.

Well, look at it this way:

Your battery puts out 12 VDC and is capable of supplying hundreds of amps to DC loads. But it only supplies the amps the loads call for. The loads have some "resistance" to current flow. In a simple DC circuit the "resistance" is actually resistance measured in ohms.

So if you connect your 12 volt battery to a lightbulb that has a resistance of 12 ohms, Ohm's Law says there will be 1 amp flowing in that circuit.
I (current) = Voltage/Resistance or 1 = 12 VDC/12 Ohms.

In more complex DC circuits that have motors and other batteries being charged the "resistance" includes the push-back from the charging battery and the Counter Electromotive Force (CEMF) of the operating motor, both of which are variable (as the battery charges its voltage increases so its "push-back" increases. As the workload on the motor increases its CEMF decreases and it draws more current to supply the load).

So when you change the range of your battery charger from say; 10 amps, to 50 amps, it does 2 things:
Raises the voltage applied to increase the current for a given battery.
Increases the ability of the charger to supply more current.

So if your battery charger applies; say, 14 VDC on the 10 amp setting, it will raise that applied voltage to; say, 16 VDC on the 50 amps setting - these are just theoretical numbers - your charger's voltage numbers may be different.

So if you are charging a battery on the 10 amp setting and it's actually only drawing 5 amps due to its state of charge ("resistance"), and you switch it to the 50 amp setting, the current will go up due to the increased applied voltage, but it won't go up to 50 amps because the battery is not dead and is still opposing the applied voltage reducing the current to what it will accept for it's state of charge.

Now unless you have a modern smart charger if you leave the battery on the 50 amp setting you will "cook" it because it can't charge to 16 VDC so the current will never decrease to 0 amps when it is fully charged.

Bottom line - get your voltmeter out and check the applied voltage on your charger on the 50 amp setting to be sure it's not ridiculously high. Remember, it's a charger, not a DC power supply.