Thanks for the reply - actually no, I did not see this post. I did massage the search function but focused on threads of the last years (since 2018). I'm surprised this was already a topic in 2010/11.
I will keep on looking for information how to revive a presumed-dead Enertia+ - even if this means a battery rebuild.
I already found the Valence U1-12XP on the net but besides the lower capacity I'm not sure it would work at all with the plus...
Are you aware of any documented battery build/rebuild of any version of the Enertia? So far I didn't find any post or video that deal with the details.