I encountered a very mint/unused 6a outfit recently. It was dated to 1928 for various reasons, notwithstanding, the 4 volt motor dates it to mid 1928, the chest and parts also date it to 1928. The set looks like it was new and basically never used! It was a joy to behold! The best thing about it was the fact that the accumulator as there! and had never been wet! That is the only reason it was still with the set. Once wet, they can not be placed back in the chest upright...it only fits laying down on its side. That is why we find so few of them today......I also came to the conclusion why the serial number on these batteries is like it is....it is so simple when you have a mint dated set....;-) More in the picture descriptors.... I would like to hear from anyone with Meccano accumulators and see their serial #'s. I would also like to find one for my own someday...if anyone has one for sale, let me know.