I think you need more battery life than the "ride time" as that will exclude all the little short stops such as getting water from a stream, toilet breaks, photos, etc. as well as the longer ones like cafe stops. My Strava times last year for an overall time of 5d2hr38 were as follows (total/moving/stops)
Day 1: 13:46 / 12:24 / 1:14
Day 2: 17:06 / 14:07 / 2:59
Day 3: 15:34 / 12:23 / 3:11
Day 4: 18:30 / 14:57 / 3:33
Day 5: 31:41 / 24:55 / 6:46
Not sure about that last one as from memory I only had three short stops (less than twenty mins each) and one longer one. But the "stops" add up to nearly 18hrs within the overall "riding time" which is getting close to my overall bivy time of 26hrs*. You could pause and restart the unit when you visit cafes/shops but given that you are going to be tired, there's a chance you'll forget - on the morning of my third day I turned on the Oregon but forgot to press "go" and actually set it recording!

Fortunately between bivy and when I realised an hour later there was only one possible route you could take so I couldn't have cheated.
So, from one data set, I'd say for a five day finish you need batteries for around 100hrs of usage plus a bit just in case.
* my third "bivy" was actually in the bothy at the OYB and from getting there to leaving was 9 hrs so that one stop was 20% of my total stopped time. Hmm. Despite the bothy being as well appointed as many regular hotel rooms it was probably the worst night's sleep I had during the event.