I also use Xtar and ask the pros are true. However some competitors charge a lot faster (I have a XMI one that can charge laptops at full speed) and are lighter/less bulky for sale capacity. Xtar is lot better in the sense you can carry a larger capacity on planes as each individual battery won't be over the limit

Just FYI in case you're not following as close as us Australians are, the submarines are not expected to be in the water for another 40 years. I will be 70+ by then