Which battery tender should I buy for winter and for long time periods I may not use my bike? I'm not knowledgeable regarding this sort of thing . . . amps, volts, etc.
I'd like something with a quick connect harness.
FWIW, I park my bike under a car port and have an outlet on a utility pole there in the elements..... for my use, having a tender that was 100% waterproof was a good idea. It so happens the Battery tender Jr I bought is such a model.
The amperage a 'smart' charger/tender provides is not a constant thing.... it is adjusted as the battery charges, to minimize any damage the charger could do to the battery. too much current into a charged battery will boil out the electrolyte, and 'sulfate' the battery plates.... that will kill the battery.
The charger starts out with ~ 14VDC, and measures how much current it needs to provide to make that voltage after 30 seconds. If it is not able to reach the 13.8 or 14VDC (depending on which model you have) it still limits how much current it will give the battery to less than an ampere, and continues to check the voltage as it replenishes the batery's charge. The various makes and models all have slightly different supply currents in the 'bulk charge' phase... but they all reduce that current flow to a much lower level when the battery reaches about 80% of it's full charge.
Once the battery is above 80% charge, smart tenders will reduce the supply current to less than 1/10th of an ampere, and finish charging at that rate. when the voltage is up to the 14.1 or so the charger will stop providing current altogether, and just monitor the voltage on a regular basis.
If the battery discharges during storage, the tender will switch back into the trickle phase, at the low current state, and 'top up' the battery. (The exact details of what starts and stops the charging process changes, vendor to vendor.... but this is what they do.)
The waterproof Jr. was the first one I found, that was waterproof, so I bought it. It was possible to buy extra quick disconnect harnesses, so I got one for the riding lawn mower, as well. I switch the charger between the two every couple of weeks during the winter.
My '05 battery is sitll working like a champ, and I completely discharged it a couple of times when I first got the bike.
Whatever brand you go with, a smart charger is a wise move, IMHO.