Battery Tenders are known to cook batteries when left connected for weeks. They're a very simple tricker charger, and old news by now. The best charger by far (that happens to be recommended by Kawasaki in the manual) is the Optimate4. What kills betteries is SULFATION. And those charges have a very effective automatic desulfation program, which significantly extends the life of any battery. I used to have Schumachers, BT+s, CTEKs, and I like this the best by far. And no modes to choose; everything is done automatically. Plus they have a special CanBUS program for BMW bikes. And they have the same SAE connections, so they worked perfectly with BT terminals. I'd trust this charger much more than a BT to be left connected all the time, but I always disconnect them when the light turns green.