Is it possible to increase the satchel size?

Question

The default satchel size is 20 items, which fills up pretty quickly by having various pokeball types and picking up items in the overworld.

Is there anyway to increase the satchel size, or am I stuck having to manage my inventory wisely?

Answer 1

Yes, it's possible.

After completing a few main quests, when you try to leave the Galaxy Hall, Bagin (the guard who stands next to the stairs from the 1st to the 2nd floor) will make an off-hand comment to come see him if you find yourself running out of satchel space.

From then on, you can talk to him to increase your satchel space by a single spot per purchase for an increasing amount of pokedollars.

The costs escalate fairly quickly though, so it seems like the intent of the developers is that you make frequent visits to the camps on the maps in order to clear up some inventory space.

The total amount of extra slots you can purchase seems to be 37, with the 37th slot costing 1 million pokedollars.

For reference, here's the price of each extra slot and the total amount you've paid by that point:

Slot #	Cost	Total
1	₽100	₽100
2	₽200	₽300
3	₽300	₽600
4	₽400	₽1,000
5	₽500	₽1,500
6	₽1,000	₽2,500
7	₽1,500	₽4,000
8	₽2,000	₽6,000
9	₽2,500	₽8,500
10	₽3,000	₽11,500
11	₽4,000	₽15,500
12	₽5,000	₽20,500
13	₽6,000	₽26,500
14	₽7,000	₽33,500
15	₽8,000	₽41,500
16	₽9,000	₽50,500
17	₽10,000	₽60,500
18	₽12,000	₽72,500
19	₽14,000	₽86,500
20	₽16,000	₽102,500
21	₽18,000	₽120,500
22	₽20,000	₽140,500
23	₽23,000	₽163,500
24	₽26,000	₽189,500
25	₽30,000	₽219,500
26	₽40,000	₽259,500
27	₽50,000	₽309,500
28	₽60,000	₽369,500
29	₽80,000	₽449,500
30	₽100,000	₽549,500
31	₽150,000	₽699,500
32	₽200,000	₽899,500
33	₽400,000	₽1,299,500
34	₽500,000	₽1,799,500
35	₽600,000	₽2,399,500
36	₽800,000	₽3,199,500
37	₽1,000,000	₽4,199,500

Source: a Gamerant.com article on the subject, corroborated by several other websites.

Answer 2

I was able to figure it out after taking to a lot of people in the village.

You can increase your satchel size by speaking to Bagin in the Galaxy Hall (first floor, right next to the stairs) at a cost.

Each purchase attributes to a single slot for your satchel. The first 5 purchases cost $100, 200, 300, $400, and $500 respectively. After the 5th purchases, the cost increases an additional $500 for each purchase: $1000, $1500, $2000, etc…