I ended up with a Power Tank Pro - a LiFePo4. It was expensive, but the discharge voltage is much flatter over time than Li-ion, and for my setup I haven't found the endurance limit yet. All I know is that for the ambient temps I have used it at so far, the limit is TBD, and somewhere beyond 6hr. And if I wanted to travel with it, it's FAA-approved for carry-on.
But I think this only works because my power needs are modest. If you were to throw, say, a cooled camera into the mix rather than a DSLR, that would be a whole different problem - and the answer would probably be lead.
Mounts: ES PMC-8 EXOS2
Scopes: SV 102EDT, ZWO 60/280 Guide
Cameras: Nikon D5300, Altair GPCAM2-IMX224C
Software: ASCOM, CdC, AstroTortilla, BYN Pro, Sharpcap, PHD2
Computer: Thinkpad x230, Win7Pro/64