I'm using lxpanel 0.6.2 and on the the batt plugin HideIfNoBattery has currently no effect. For example setting this option to 1 on a computer without a battery results that the plugin is still visible in the panel (but it does successfully notice that the computer doesn't have a battery).
I believe this issue is completely fixed in latest version of LXPanel - 0.7.0. Try it, please, and let us know if something is still wrong. Thank you very much.