To check what is the 2014 Dyna H-D AGM Original battery Ah?
I have a battery charger (CTEK MXS 5.0) that has an option to choose 0.8A (1.2-14Ah) or 5A (14-160Ah) to charge the battery
If the H-D AGM Original battery is 16Ah, is it ok to choose 5A to charge the battery? Or it is better to be safe to choose 0.8A for longer battery life. One of the concern is 0.8A may take a very long time to charge compare to 5A
Just like it is not recommend to use the ipad charger (2.1 Amps) to charge the iphone (1 Amp)

 

a very lot has to do with the charger itself. if the charger is of a smart type that can regulate current and then go into float or maintenance mode then the issue becomes of little value.
there is one cravat in that some vehicles have parasitic draw and even a smart charger can be tricked into not going into maintenance mode so the recommended rate for small batteries is in the 1.5 > 2.0 range. even a small 2 amp charger can cook the water out of a cell. the issue with iphones and such is more along the lines of creating excess heat with the ion batteries which can lead to fire/explosion. once again, there are smart charge stations that can sense and adjust current since they are designed for multiple devises and products, you see these popping up in public areas like hospital waiting areas.

 

The two optional chargers you mention sound like (1) a low power tender type and (2) a higher power charger. The low power one is suitable for maintaining a battery, such as periods when the vehicle is not being used, the other one would be more useful for charging a discharged battery.

I recommend you spend a little more time checking what is available to you, also what you need. I have several low power tenders, all working as I write as it's winter here and I don't ride when it's freezing! I also have a proper battery charger, for those few occasions when I want to charge a discharged battery. The latter is not very often, thanks to my tenders.

If you buy a tender, otherwise known as a battery minder, make sure you get one which regulates itself, as suggested by bustert.

 

Why don't you get an intelligent charger that can do both ( charging & tender). Really makes it easier and you just need to plug it to the battery and done with it. The charger will select the charging-modes as the charging process continues.

 

A charger is only used for a very low charged battery. Don't use it to maintain a battery, and font use a trick.e charger. For long term care, use a Battery Tender.

And you're wrong about the iPad & iPhone analogy. Current is not pushed...it is pulled. Think of it as capacity. Your device will lull what it needs. Do, if anything, make sure you adapter has enough capacity.