I get around 6-7 days on my 312, depending on how many calls I make.
Only one pack is needed at any one time, I guess if your a little paranoid about it you’ll have stashes all over the place, but just one pack for me.
For me if would have to be 5 to 7 days before I’d bother. Having to charge every night and having to carry a recharge pack when out hiking and away from the grid… it’s just a hassle. Plus I don’t like the fact you have no hearing while they are doing a quick 10 or 15min charge.
It’s just one pack in your pocket wherever you go, just like having coins in your pocket, you just don’t notice it, no need to have stashes all over the place ; )
Excellent choice the size 13 battery is definitely the way to go.