I've been running a WPS I bought on eBay for about a year in my S1000rr. Super light, no problems to report. Cold starts are different, you have to key on the bike and let the battery warm up running the lights and guages for a moment - and it will fire up strong. If you don't wait, it will sputter and stall. That, apparently, is the nature of LI batteries.
I will add to my other two bikes as their lead acid batteries shows signs of expiring.
WPS Featherweight Lithium Battery HJTZ10S-FP-IL | eBay
Kevin M.
2010 HP2 Sport
2010 S1000rr
2007 R1200s