I side w/Morris9982 - Deltran (Battery Tender) makes HD's units and multi-bank would be best for your situation. Been using HD's for couple of seasons w/no problems.

 

I have used a Battery tender since 89. Have the same one. JP cycle has some that do mutiple batteries ,but they is pricey. I think you would be better off just buying one for each bike. I would look at the Schumacher that Inspector 12 recomended. Batteries do last longer if charged. Tenders no matter who makes them do not overcharge and cook the battery.
http://www.jpcycles.com/battery-tender

 

I have this and I'm very happy with it.

 

One thing to keep in mind the older Deltran Battery Tenders are not designed for use with the newer AGM batteries as someone else mentioned. I've read their technical sheets on their web site and it has something to do with the float time between the initial charge and switching over to the maintenance mode.

I have one of the original ones and it just switches from red to green. I use this one on a car. I have one of the newer ones on my bike and it has a three stage charge cycle, solid red, flashing green, and solid green.

If I had four bikes or cars to maintain I think I'd get one of the Battery Tender Plus models or the Schumacher one for each vehicle. It would end up costing you less.

 

I have a sears automotive battery charger that will shut down to trickle charge after full charge,,I made an adaptor that fits the charge plug on my ultra,,,if it sits for a long period of time I hook it up,,,switch it to 2 amps and let it run for a day or two,,,works great and i don't see any reason it wouldn't work on several batteries ant one time...

 

whew!!! i may be more confused than ever.. i may buy several of the smaller ones (+/_$8.00) or one of the multiple battery jobs. several of the cheapies would be easier to reach different bikes, if i put more outlets in the unheated building where i keep the bikes, or one of the multi's with lots of jumpers. i will have to dom some shopinmg before i decide. thanks.

 

Keep in mind that you can buy extensions to lengthen the wires that go from the charger to the bike. I'm pretty sure my HD dealer keeps 12' and 25' ones in stock. There may be other lengths available or you could piggy back them.

That way you could keep all your chargers in one place and just run wires to the bikes.

 

Battery Tender Jr. here too. It's been 2 years of trouble free battery maintenance for me!

 

One option you may have is to buy 2 tenders and just move them around the different bikes every 7-10 days. They will hold a good charge for that long if the batteries aren't too beat already.

 

I use a HF one on my PWC battery (wet cell) and a BT Jr on my bikes AGM