Those hoping to fully upgrade Link's Energy Cells in The Legend of Zelda: Tears of the Kingdom are going to have to get their hands on an awful lot of Crystallized Charges. These rare items are typically traded for Zonaite at Forges and then taken to special Crystal Refineries like the one just north of Lookout Landing to be processed into Energy Wells.
Three Energy Wells make up one full Energy Cell, meaning that players will need to get their hands on 21 of them in order to go from the single cell that they start with to the maximum of sixteen. Unfortunately, even if players manage to find a way to reliably farm 
Zonaite, they'll find that trading it for Crystallized Charges can be a time-consuming process without this simple method for restocking Forge Constructs in The Legend of Zelda: Tears of the Kingdom.
How to Restock Forge Constructs in Tears of the Kingdom (How to Get More Crystallized Charges)
Each Forge has a slightly different inventory, with some stocking more charges than others. Whichever they choose, though, players will find that there's a limit, meaning that they'll only be able to get their hands on a certain amount of charges at a time. Thankfully, however, there's a very simple method for forcing Forge Constructs to replenish their inventories, allowing those who have enough Zonaite to trade for hundreds of Crystallized Charges in a matter of minutes.
Although this method will work at any Forge, it's best to use it at the one in the Great Abandoned Central Mine. This is because as well as players being able to fast travel there after their first visit, it also has a fairly sizeable inventory, with five large Crystallized Charges available as well as 30 small ones. This means that players can get as many as 130 Crystallized Charges each time the Forge Construct restocks, which can make maxing out Link's Energy Cells a real breeze.
To restock the Forge, players will need to advance the day by one then save and reload. To advance time quickly, they can simply drop a stack of wood on the lava coming out of the forge so that it sets alight and then sit by the fire until morning. As soon as the rest animation has ended, they can open up the menu, save the game, then load that same save file up to restock the Forge's inventory. They can then rinse and repeat as many times as needed.
How to Max Out Link's Energy Cells in Tears of the Kingdom
Players will start the game with one full Energy Cell, meaning that they'll need to acquire fifteen more in order to reach the maximum of sixteen. This translates to 45 Energy Wells, which will require 4,500 Crystallized Charges. Players can trade these for a combination of Zonaite and Large Zonaite, with 15 Large Zonaite needed for five Large Crystallized Charges. As five Large Crystallized Charges are worth 100 regular charges, players can max out Link's Energy Cells with 675 Large Zonaite, which would require restocking the Forge Construct's inventory no less than 45 times. After reaching the maximum number of batteries, players will unlock the ability to buy Zonai Devices with any remaining Crystallized Charges they may have.
Sadly, players can't use Tears of the Kingdom item duplication glitches to dupe Crystallized Charges, but they can use them to get more Large Zonaite. As a result, those who are still able to use the glitches can max out Link's Energy Cells fairly quickly by using the Forge Construct restocking method detailed above.
The Legend of Zelda: Tears of the Kingdom is available for the Nintendo Switch.