Bumping thread to add:
I just sent mine back to Tekkeon today for either service or replacement today. It started rapidly dropping from full charge to no charge it was able to provide power for a whole show, but not without worry. It's only a little over a year old and was issued after their charger recall, but it looks like there may be a circuitry problem that affects performance.
Been happy with it until this problem started to surface in June/July. Noticed other tapers have had similar issues outside of warranty and Tekkeon has been good about replacing them so we'll see how this turns out. Probably too soon to tell if anyone has had problems with a replacement battery yet. If a replacement battery develops the same problem after only one year I don't think I'd get another one.
fwiw: My model is a myPower ALL plus external laptop battery [MP3450 R2], not the industrial version. It was ordered from Amazon not a 3rd party Amazon seller. Its voltage is only selected manually via the top button, it does not have automatic voltage selection or dip switches. It does automatically default to 5V to help prevent over voltage and locks to the voltage you select once you've connected it to the device you are powering. Apparently there are different versions or some models have automatic voltage selection which some people have and has given them voltage problems.