Charging rate elec question

path1 wrote:
Thinking about upgrading elec system because I keep having little problems with connections and cables etc. If I upgrade I'm going to put in a "smart charger". Talking with a guy at battery shop and got me confused and here is question:

A good "charge rate" is 10 - 20 percent of Amp hour rating of battery?

He went on to say, don't go over 25 percent as it actually bad for the battery. I'm pretty sure I heard him right. Any truth to this?
Reason I ask is: won't a "smart chargers" know how much to charge for the battery(s)that I have?
(OK you can tell by question elec is not one of my finer points).

the charger does not know if its connected to a 12amphr motorcycle battery or 8 big deep cycle batteries for 1000amp hrs

all the smart charger know is how much resistance is in the circuit aka how many AMPS the batteries are taking, it doesn't know if they can only accept 5amps or 200 amps

it can only check the battery voltage against how many amps the batteries are taking
it will stop periodically to do battery voltage checks