I am trying to decide on a storage meduim for a modest trailer-mounted system using a 3kw48volt all-in-one. I value simplicity and low maintenance over maximum efficiency. To that end I thought I remembered reading about a sodium/lead battery design with the energy density of lead acid but none of the nasty issues (monthly maintenance, corrosiveness, etc). As I recall, 100-amp/hr 12-volt weighed around 100 lbs and cost around $500. When I got ready to pull the trigger on a set, I can't seem to find them anywhere....did I dream them?