From threads in these ng's I've come to the conclusion that most chargers
do
not top off the batteries. Is that correct? There must be some commercial
off the shelf chargers that can do the topping off?

I keep my two 12v batteries topped off and desulphated using the little
Battery Minder by VDC. I've had it for a couple years now. My batteries
were connected to it all last winter with no loss of battery fluid. I got
mine at Northern Tools. Here's a link to the product:
http://www.northerntool.com/webapp/w...012&R=197 012

also if you're interested in desulphation, here's a link to the topic at
VDC's site:
http://www.vdcelectronics.com/desulphation.htm