I have been reading everyone's battery suggestions and I thought I would add a bit of data to the mix.
I installed a power meter on my PMC-8 Exos2 so that I could see my total current draw from 12 volts. I am powering 2 heater strips, the PMC-8 box, my TEC camera (QHY163c) and a guide camera (QHY5L-ii). The current draw is 3.5 amps maximum with 100% TEC power applied. When I turn off TEC cooling my current draw is 1.6A. Obviously, TEC cooling takes a lot of power! The two heater strips are using 0.7A. So to power my rig for say 6 hours it would take a 6*3.5 = 21 A hr. Without TEC it would be 6*1.6 or 10A hr. Hopefully this will give you some ballpark numbers to use when choosing a battery size.
Hope this helps,
Mount: Explore Scientific Exos-2
Scope: Explore Scientific ED102CF
Filter: Optolong L-eNhance 2" for nebula pictures
Software: ASCOM, PHD2, CDC, Sharpcap Pro
Computer: Dell desktop XPS
Extras: Lots of 3D printed parts I designed to improve usability