First of all, go to Amazon.com and look up “Hearing Aid Battery Caddy”. There are several brands that attach to a key ring. Instead of chaining it to my keys, I personally chained mine to a couple of USB Thumb Drives and an electronic office door key that I carry with me all the time in my pocket.
Secondly, get to know that average life of your brand of battery, then get in the habit of changing them at specific scheduled times before they run out, rather than trying to get all the goodie out of them. Even with spares in your pocket, it’s far better to waste a bit of battery than to have to interrupt a conversation for an unscheduled battery change.
My older Pure700 aids use 312 batteries and with my normal use and programs, they will consistently run 8 days, so they get changed every Monday morning before I go to work. (Seven days use).
Most of the time now I’m wearing my Aquaris models which use size 13 batteries, and I consistently get about 15 to 16 days, so they get changed every other Friday (Payday), for worry free performance. To maintain fresh spares, I always use the ones in my caddy to replace the ones in my aids, then refill the caddy from the pack at home.