Here is my take, What happens to the battery that is fully charged first? The charger will run until both are fully charged. If the batteries are hooked up in series or in parallel that is different. If you dont want to pay for a second tender then move it back in forth weekly.

 

I had one tender(plus model) and two batteries, just moved the cables from one to the next every few weeks. Then I bought another tender, the Jr. this time. They're not very expensive.

 

I suggest you move the charger back and forth as brewmany suggested. I've been doing this for years with no problems.
I'm pretty sure you'd have potential issues with a 'smart' tender and two batteries wired in parallel.

 

I hooked my tender up to both bikes and it blew the fuse in the tender

 

Like boats, RVs, and hybrid vehicles, as long as the batteries are wired in parallel and the charger/tender/maintainer can deliver the amperage needed to charge, it's fine using one charger.
Does nothing to the under/over charged battery because as soon as you hook them up in parallel they will equalize and the difference of potential will be eliminated.

That is if you can get both batteries in parallel properly...

 

as a few others have noted, just switch between bikes every few days. I've done that for years with no problems and always keep the batteries fully charged.

 

A Battery Tender Jr. is only $24 shipped on Amazon.


For me, that's a no brainer to keep from rigging things or having to swap every week or two. Why spend 20K on a bike, and not be willing to spend another $24.00?


Maybe it's just me, and it's certainly just my opinion, but that makes no sense. Maintaining my bike is not an area where I pinch pennies. Each to their own though, it's not my place to judge other's decisions.

 

I have one HD Smart Charger, and move it around to all my batteries.
I like it this way, different strokes for different folks.

 

Battery tender 2 bank