As we further adopt professional V-Mount and Gold Mount batteries as our primary power source, we have discontinued selling The eMotimo 23000 mAh battery.
If you are looking for an inexpensive portable pack to power your spectrum, we have found these to be a reliable.
The sized packs provide your spectrum ST4 with 5-8 hours of shooting depending on your motor move profile and the number of motors being powered.
Also, we are trying these packs out internally, but look very promising and have about double the rated capacity of the above battery.
For more information about external batteries check out this article on powering your spectrum.