Battery Chargers

[Ryank]

Just a question, Hopefully someone knows an answer to. I have an older Bomar battery charger in like new shape. It charges great, and when it's done, goes into a "float mode" where the amp needle bounces around from 0-5 or so. The voltage ouptut is still 13.4 volts. I was concerned this would overcharge batteries so I looked at new chargers. They seem to do the same thing go into a "float mode" with an ouput still of 13.4 volts. Is the voltage continualy feeding into the battery at 13.4 harmful and will it cause overcharging or is it the amperage that is harmful to batteries therefore making my charger ok to still use?