Welcome to Android Central! There's no such thing as a battery virus--it's a popup that is most likely associated with the website you're visiting, and it's trying to lure you into installing something that is almost certainly malicious. DO NOT TAP ON ANYTHING IN THAT POPUP. You need to avoid that website in general. For good measure, go to Settings>Apps>All, select Chrome, and Clear Cache/Clear Data, then Force Stop. Open Chrome again, tap Menu>Settings>Privacy, scroll all the way down, tap Clear Browsing Data, and clear your Browsing History, Cache, Cookies/Site Data. Now see if the problem persists.