If you have more than one Sneaker or Headset, you can shelve a Sneaker or a Headset to increase your available energy supply and get more traits. The more Sneakers/Headsets you shelve, the more Energy or Charge you get.
The amount of Energy/Charge you get depends on the sum of the base attributes of your gear. The higher the sum of your Sneaker's/Headset's attributes, the more units of Energy/Charge you can get.
The full Energy/Charge supply is based on the base attributes of the Sneakers and the Headsets on the shelf.
The additional attributes do not impact the calculation of the energy supply.
The sum of all the sneakers' base attributes of 28 units gives 11 energy units,
The sum of all the sneakers' base attributes of 48 gives 15 energy units,
The sum of all the sneakers' base attributes of 100 units gives 26 energy units.
Once you have put a sneaker or headset on the shelf, it cannot be returned. The sneaker/headset trait 'Trade Orders', which affects the number of items that can be placed on the marketplace, will continue to work, other traits are applicable only to the sneaker/headset they initially belong to. So, choose wisely which to train in and which to store on the shelf.
Read more about Bonus Energy and Bonus Charge in these articles: