use them on every thing, the harley,the side x side, even my truck(have company van, can go weeks without starting it). i use the cheaper Peak brand one you can find at Menards for about $20.
Well, I was trying to insert a picture of the Optimate 3+ Battery tender that came with our newer Yamaha sleds ('06 & '07). Here is a link to a vendor:
I also have one that is solar I bought from Harbor Freight. Charger was $14 and the regulator was $27, I use this one on my lawn tractor. My other solar doesn't have a regulator and it can overheat the battery, boiling out the liquid.
Our other trickle charger is a Tender Jr.; don't remember how much it was, but these have been working fine for the last three years. Knock-on-wood, haven't had to replace a battery on our 4-strokes, yet.
I have at least 11 (that I can remember), from the solar to onboard mounted. The best is the Battery Tender because it is either charging or off. Some of the others put a trickle charge which over time can shorten the life of the battery. I do have a 15 year old Craftsmen that not only charges (up to 10 amps) but will periodically load test the battery. If the battery is questionable, an alarm sounds until you reset. This one has been in use 15years on my battery backup sump pump. The 10 amp will run the sump if the battery is no good. Wish I could find more like it.