In this guide, you will come to know how to get the Ion Battery and Ion Power Cell Blueprint in Subnautica.
Starting from the coral tube sticking up out of the water, you will need to make your way about one bump or 1 in a half bump to the right of northeast until you reach a large drop with a large cave entrance in the bulb zone.
It is recommended to have a cyclops with a Grapple arm and Mk1 Depth Module, a sea glide, a high capacity O2 tank, a reinforced dive suit, and a survival knife.
The main threat you will encounter in the inactive lava zone is the sea dragon Leviathan, you have to avoid them, and the lava lizard, you can either avoid or kill using the stasis rifle and survival knife. You will also encounter the warper, which can warp you out of your vehicle; you can run away from it or deal enough damage to it, so it warps away.
There are also lava larva in the inactive lava zone; if you bring your cyclops down there, they will try to latch onto your cyclops and drain energy from it. If one latches on, you can use your knife to cut it off your vehicle.
The coordinates for this location are (-75, -1182, 5).
You will also need at least one purple tablet to unlock the door to the blue tablet.
Here is the large drop and entrance you are looking for.
Once you’ve gone through the large entryway, you will need to continue heading down the entryway, and you should eventually come across a large hole in the ground. You have to go down in, and it will lead you to the inactive lava zone.
There is a ghost leviathan near the hole, so you must try to keep your distance from it as you are heading down into the hole.
Here is the large hole you are looking for.
Once you are in the inactive lava zone, you will see a large open area like this. You have to continue straight, and you will come across the lava castle at the entrance of the large area.
Once you’ve reached the lava castle, you will need to look around the sides of the castle for a small entrance with some green pillars with lights on it. It will lead you inside the lava castle.