The more complicated your builds in The Legend of Zelda: Tears of the Kingdom are, the more demanding they will be on your battery. You may think you're fine with only three or four complete Energy Cells, but that's only until you attach six fans together to try and race up Death Mountain as fast as possible.
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If you're trying to reach the height limit on a Hoverbike, you'll run out of energy long before you're prepared, so trying to make your batteries last for as long as possible and get the most out of them as physically possible is important. Building can be fun, but only if you have the juice to keep those builds going.
Worst comes to worst, all you have to do is buy some Crystallized Charges from one of the many Abandoned Zonaite Mines found in various parts of the Depths. For every three Large Zonaite, you can buy one Large Crystallized Charge, which is worth 20 of the standard Crystallized Charges.
The Standard Crystallized Charges can be purchased for three of the standard Zonaite. For every 100 Crystallized Charges you collect, you can forge one Energy Cell, though it takes 300 to make a full battery. This is probably the most conventional and least fun way to extend your battery power.
You can farm up a bunch of Zonaite from the Depths and max out your battery capacity, but that really won't extend how long each battery can be used for or milk each Energy Cell for everything it's worth.
Fighting the Zonai Flux Constructs scattered throughout the Sky Islands won't necessarily drop you any batteries, but you will get Crystallized Charges. This is a great way to farm up a sizable amount of Crystallized Charges specifically because you don't have to run around and collect a bunch of Zonaite, and it can be done once every Blood Moon.
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Fighting the Flux Constructs is significantly more fun than running around the Depths trying to get your hands on Zonaite. All you have to do is be a little creative with your Ultrahand to drag off the blocks and its power block, and suddenly, the fight is a breeze.
Attaching External Batteries, both large and small, is a great way to keep your vehicles and builds going for a little bit longer. As mentioned, they come in both large and small sizes, and with most things in Tears of the Kingdom, the larger size is the heavier one.
This means that, generally, you must be very careful with your placements because once it runs out, it disappears and will change the weight balance of anything you build. Regardless, so long as these external batteries are properly fused to your builds, they will drain before the build starts tapping into your personal charges.
Unfortunately, the only thing that external batteries don't work on is Mineru's construct.
This is by far the easiest and fastest way to replenish your batteries, and you don't even have to wait for them to run out before you do it. The only downside is that you have to fight the Soldier regularly and Captain Constructs or participate in the Zonai challenges if you want to refill your stash.
Of course, you can always buy them with Zonaite, but that should really be saved for buying the Crystallized Charges. The Small Charges will only partially refill your battery, but the Large Charges will refill it and then some.
The Large Charge should give you an extra "bonus" battery that will run out slightly slower than the standard batteries - however, this bonus charge will disappear if you don't use it (so get use it for everything that it's worth!)
The Zonaite Armor is a bit of a pain to get, but once you have your hands on it, you can wring every drop out of your batteries, and it'll take even longer than usual to do it. For one reason or another, the Zonaite Armor makes the charge on your batteries last longer, whether it's because you're in harmony with the Zonai Devices like the descriptions on this armor set seems to imply, or if it's because of strange game logic is up for debate.
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Regardless, if you're struggling to make your batteries last as long as possible, then the Zonaite Armor is a must-have. To get the leg piece, you need to complete the puzzle and grab the chest in the Akkala Sky Mines.
For the chest piece, you'll need to complete the puzzle on the Zonai Forge Island (this one is fairly easy to figure out once you activate it at the dragon ring). The headpiece requires you to reach Lightcast Island near the Tabantha Sky Archipelago and solve the puzzle activated by the dragon ring.
This is a little bit of an odd one, but in order to see it in action, you need to attach a Zonai Portable Pot to your build. It doesn't really matter where, so long as you can use it to cook a meal (or anything, really) when the time comes.
As you're running out of power and your battery is almost depleted, gather up your materials in your inventory and quickly throw them into the pot to cook - but make sure you do this before your battery dies. When the cutscene has ended, you'll come back to your batteries fully charged, and you'll be ready to go for even longer (or at least until the Zonai devices despawn).
You'll have to attach another pot if you want to use this method again on the same device, however, considering that the Zonai Portable Pots are one-time use only.
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