You'll have to expand on which online batteries and what you mean about not lasting?

The factory battery in my 660 Grizzly lasted maybe 5 years with plenty of care (kept charged and warm when not using it). It was a straight-up Asian battery and they really all look identical whether you get them from Walmart, the Dealer, or online?

I'm on year 4 of a Lithium ion, so can't say yet if it's a better battery, but it sure works like new.

As far as cranking power, check your connections: my Grizzly is very tempermental on connections. More than once I thought my battery was done and a good cleaning of the positive ring got it going again.