Again it it alters due to how long your out.
I only get 2x10 hour days plus time enough to plug the next days ride in by hand off a pair of AA rechargeables in my Garmin 30 when not powered by the dynamo.
So 4 batteries each recharged once will last me for a week tour.
So a big cache battery will easily do that plus a couple of charges on my kindle will and also a bit on the phone as needed.
If I was going out for longer than a week then 2 or 3 cheap cache batteries may well better.
You will have to recharge them more often than 1 big one, but it a lot less of a disaster if one dies or goes missing.
The most expensive part I use where recharging in a toilet block may be the USB cable.
I did this on a 4 month tour before I got my solar panel/hub dynamo combo working.
In western Europe I was grabbing power in campsites, in eastern Europe it was 6 nights wild camping and then 1 night in a hotel to recharge everything.
It's just that a solar panel and/or hub dynamo makes it a lot less hassle.
Luck ..........