The 15 AH NORSK is perfect. You’ll never run that battery out of power in a day. A 10AH is too small IMO if you put in some long hours. I’ve been using that battery in all my Helix units since they came out 4 seasons ago and they’ve been super reliable.
I run a 10 on my Helix 7 and can get a “full” day out of it. Specs say 12 hour runtime. But, certainly wouldn’t hurt to go with the highest capacity you can fit in your shuttle.
If you don’t have a shuttle go with the Marcum shuttle (12 amp). I did that this year…well is ready to go whenever I can find a transducer. Marcum shuttle is a nice package. Just need a spacer. If you go that route pm me I can help you out with spacer. I just did it on mine and have files saved.