I have that Jackery 240 and can say it's an amazing bit of kit. I decided not to look at deep cycle marine batteries. Too many things to consider, especially about keeping it above a certain power level.
Jackery is also slightly expensive, and you can do the same thing (I've also got this) with a LiFe Po4 battery, and adapters to your mount. I bought the adapters from Jaycar for cheap. The battery cost $110.
LiFe Po4 is also a lithium battery (not the same as the Jackery) and will give you more recharge cycles than marine batterys, is MUCH lighter, easier to carry, smaller, and can discharge to a smaller capacity.
If you're new to this, I recommend staying away from the old tech, and embrace the new
PM me if you want pictures of the battery setup, happy to show more if you want.
edit: forgot to add, Jackery is a
regulated 12V lithium power bank. That means you will get 12V minimum (usually circa 13v) no matter the capacity. Other lithium batteries will drop voltage as you use the battery. For my mount (EQ6-R) a stable power supply is a must.
There is another power bank coming called the Bluetti AC50S (not to be confused with the older AC50) that is also regulated. It's out in the UK and US and Japan, but no local adapters yet. It will also charge faster than the Jackery, which is the Jackery's only main problem (mains charging peaks at 48W). I've been chasing the company to release an Aussie version, which they will do but they are slow.