is there a way to plug the 8130 in usb and tell it not to charge the unit??

I don't think so, unless you remove the driver that is used to charge the device. I believe the only way to do that possibly is remove the Desktop Manager, maybe.

In Device Manager, figure out which port the blackberry is connected and either power it off or disable it.

I'm curious why you would want to do this.

"I'm curious why you would want to do this."

I just needing to plug in to sync, then unplug to access mem card then plug in again, rarely getting to full charge. I am one who still believes in running the batt. down complete before charging.

"In Device Manager, figure out which port the blackberry is connected and either power it off or disable it."

If I disable it, will I be able to use the device manager??

If you disable the port, no communication.

You will not hurt your battery in any way if you let it charge for a bit while syncing or accessing your mem card...and I don't think there's any option to disable charging that won't also disable communication.