I connect the RPi with a ASI120MM-S and an ASI533MC attached and a OnStep mount driver (consumes below 2A) and I've been able to run the setup for more that 6h
About the ASI533MC: the cooling is connected to a second battery. If I try to connect the cooler to a single battery, I overload it and it stops. So the easy solution was to use a second battery (of the same kind) to run the cooler.