As @TDunn noted, the only currently available external power options for the ECOTI are very pricey.
Yes--there are a number of accessories and adapters that have been made over the years, such as AN/PVS-24 and -30 mounts, etc., however current availability is somewhat of a different issue.
Optics 1 isn't really set up for individual commercial sales, hence why we have partnered with them to make these products available, however they are not really in the business of building parts in onsies and twosies, short of a major contract requirement. This means that there are a lot of prototype capabilities that are hypothetically possible if there is an ongoing requirement, however that does not mean that they are readily available.
We have been working closely with Optics 1 about power solutions as we recognize that there is demand for such a product. We will announce these when they are ready, however in the interests of setting appropriate expectations, I cannot and will not give any kind of ETA on the availability of such products.
What I will say is that having used the ECOTI now for quite some time and having the external power options available to me, I still rarely use the external power options, and usually opt to use the onboard battery most of the time.
View with the GPS Battery Pack connected (exact location obscured for OPSEC purposes
):
~Augee