The Wood Mining Cell was removed from the crafting tree with update R39 on February 22nd 2017, however while the crafting recipe did not exist any longer (along with the rare Recipe for the Charged Wood Mining Cell), the common Wood Mining Cell could still be obtained by Keepas. This has been fixed shortly afterwards.
Power Cells seem to power up and "transform" the arctek-gauntlet that the player character is wearing on their right forearm, which seems to be the actual harvesting-tool.
With the Wood Mining Cell you can mine Stone or Fossils, and of course all "weaker" surface blocks like Grass, Dirt, Wood and vegetal materials. To pick up / dig through even harder rocks like Bedrock and Limestone you will need Stone Mining Cells or better ones though.
Other than that you were able to craft Wood Mining Cells before update R39 yourself in your Crafting Menu (default key "Q") or at any old Crafting Table (that you might still find in older worlds created before R22 on September 16th 2015).
The crafting-recipe for Wood Mining Cell was one of the starting recipes already known/unlocked at the beginning of the game.
To craft 1 Wood Mining Cell, you once needed (until R39 in February 2017):
- 4 blocks of any kind of natural uncorrupted Wood from any tree or Log (the small golden arrows indicate that you can browse through alternative materials) as can be found in most surface Biomes
- 1 Red Mushroom that you can find growing on the ground in Woodlands, Forests and Grassland biomes, or else in the Loot Bags of aggressive BossHogs - or as a harvest if you have tamed and fed these Creatures as your Pets
- 1x Vines, taken from Cragwood-trees in the Forest or Woodlands, or from Wildwood-trees in the Jungle or from the Loot Bags from many kinds of Leafies - or as a harvest from Pet Leafies after you have tamed and fed these Creatures
Whenever you use the Wood Mining Cell to pull/mine/harvest materials, the Mining Cell will lose durability until it falls apart.
Wood Mining Cells will only lose some of their durability when pulling Dirt, Grass-blocks of any kind and vegetative materials like Wood, Red/Brown mushrooms, Vines and Plants (which you could also harvest without needing any Power Cells), however they will lose even more (the double amount) of their durability when pulling Stone, Fossils and equally hard materials/rocks.
To be precisely: one Wood Mining Cell can pull 280 blocks of Stone and/or Fossils until it has worn out completely, or 560 blocks of Wood, Dirt, plants and vegetational material (as of R24 in in November 2015).
You cannot pull any harder rocks than Stone with Wood Mining Cells - like Bedrock, Limestone or Magnetite on the Fossil Layer, nor caramel Canyonstone, red Ruddy Canyonstone, maroon Dark Canyonstone, Peakstone, Ice, Ice Slopes or Mold. For that you will need better Power Cells, made from materials that your Wood Mining Cell can help you harvest.
Obtaining Wood Mining Cells was one of the requirements needed to unlock the crafting recipe for the better Stone Mining Cells (that can mine/harvest/pull harder materials/rocks, as can be found on the Fossil layer underground). It was also necessary to craft the very important Processor and (basic) Extractors that are necessary to extract Ores from Nodes, starting with Coal and Obsidian.
As described above some materials needed for crafting recipes have alternatives. This is indicated by small golden arrows on the icons of these "ingredients", like Wood for these Wood Mining Cells.