I've never had any luck getting my bots to use dedicated charging ports. They always seem to ignore them and just queue up at their respective Roboports.

Putting them in or along high traffic areas is generally how they're used. The more bots that need charging in an area or along a path the more useful this becomes. Been using it in a base with 17k bots right now and it's been very handy.

I eventually figured it out. Bots will only use the charging station if they run out of power IN THE MIDDLE of a task, that they need additional power to perform. At that point, they'll recharge at the nearest source available. If bots have concluded their work and have decided to "go home" they'll ignore all the charging stations and pile up at the Roboport. That's what was throwing me off, it seems.