Not saying that you don't have a starting issue, but if you're new to the Tenere, everything might be ok. My neighbor says I need a new battery every time he hears mine start. And compared to his Gold Wing, mine does sound sluggish. His starter sounds like it's going to jump out of the bike. But mine sounds the same today as she did on the first day. So, if your last bike had a fast-turning starter, everything might still be ok.
But if you want to go lithium, it's the same model number as the OE AGM; YTZ12S. That being said, most people upgrade to the YTZ14S for the increased amps. Just Google YTZ14S lithium and pick one.
So the battery I have is probably a year old. I always have it plugged into the trickle charger when not in use.
Last night I was out on an overnight trip, and we had freezing temps overnight. The bike would not start in the morning. It would crank, but the display would go blank while cranking, which I guess means there wasn't enough juice going to the ECU. I took the battery out and went to like 4 different stores but none had this battery in stock. The Autozone battery tester reported a bad battery with 64CCA only. I did not know YTZ14S work also work, so I bought a jumper cable as a last resort.
After jumping the battery, I rode it for about an hour and had to stop to fill up. After stopping the engine, it cranked up instantly.
When I got home and plugged it into my trickle charger, the green light on the charger came on in about 30 seconds. But perhaps it still does not have enough CCAs for cold weather?
Anyways, since its always been a sluggish crank, even when I had the battery new, I'd like to try a lithium one now with higher CCA.