I have been shooting with the R5 for about a year and I am very satisfied with my decision to skip the grip. Honestly, the Canon BG-R10 Battery Grip is a bit of a luxury that you just dont need when money is tight. For a wedding in Seattle, you will definitely appreciate a lighter setup. There are two reasons why I suggest sticking to batteries:

• Weight management: Extra cells are easier on your wrists than a bulky body.
• Cost: You can buy several spares for the price of one grip. I usually carry three Canon LP-E6NH Lithium-Ion Battery spares and it works well for a 10 hour day. If you want to save even more, I have had no complaints using the Watson LP-E6NH Li-Ion Battery Pack which is much cheaper than the official ones. They hold a charge great and feel very reliable.

Late to the party but since its a Seattle wedding, worry more about the moisture. Id grab a Peak Design Shell Rain Cover Medium so you dont risk the electronics if it pours. Also, check out the R5 heat management guides on the Canon Rumors site before the big day. Definitely pick up an Expert Shield Glass Screen Protector for Canon R5 to avoid scratches from buttons while the cameras hanging.

I would suggest focusing on your storage instead of the grip. Those R5 files are monsters, especially for a wedding. Be careful with slow media or your camera might lock up mid-ceremony and you wont be happy.

• Make sure to get a SanDisk 128GB Extreme PRO CFexpress Type B for that fast slot.
• You might want to consider the ProGrade Digital CFexpress Type B and SD UHS-II Dual-Slot Reader so you arent waiting all night.

Honestly saw this earlier but just now getting a chance to weigh in. Man, the state of the pro market right now is just exhausting. You shell out four grand for an R5 and then Canon basically expects you to hand over your firstborn just for some extra power or a plastic grip. It drives me crazy how these companies have turned basic gear into such a blatant cash grab. I was reading some threads over on the Fred Miranda forums and the DPReview archives about this... people are just as fed up with the Canon tax as I am. Unfortunately, the build quality on these modern accessories doesnt even feel as solid as the old 5D era stuff, yet they charge double. Its such a scam. Sony and Nikon are basically the same, the whole industry just assumes were all made of money. It really sucks when youre prepping for a wedding and getting nickeled and dimed at every turn.