This tutorial will teach you how to properly use batteries and energy crystals.
RE Battery
The empty RE Battery is crafted from 3 tin ingots , a single redstone dust and 2 cables .
After crafted, you can charge the RE Battery in the upper slot of a Generator , Nuclear Reactor , MFE Transmitter , MFS Unit and any other kind of generator (including the weakest of them, the wind mill).
When the battery is charged, you can use it on the lower slot of machines such as the Macerator , Electro Furnace , Mobile Charger ... The battery discharges INSTANTLY!
Or place it on the bottom slot of a MFE Transmitter or MFS Unit to discharge it to the power storage of the MFE/MFS.
Uncharged batteries stack in up to 16, charged ones can't stack.
But to stack charged batteries, you can craft battery packs out of 6 charged batteries and 3 tin ingots, which pop 6 charged batteries and disappear when right-clicked.
Single-Use Battery
The Single-Use Battery, like its name says, can only be used once until they disappear, and store the same power (10000 EU) as RE Batteries.
It is crafted from a single cable and 2 fuel or bio fuel. The difference between fuel and bio fuel is the number of batteries crafted:
Unlike RE Batteries, they will always stack, and up to 64.
Bat-Pack
The Bat-Pack allows your electric tools (that ones which you charge with the Mobile Charger - not the Mining Laser!) to obtain power off a simple battery you wear as armor. It can store 60000 EU.
Craft it from 3 charged RE batteries, a single tin ingot and 2 cables:
After crafted, put it in your hands, RIGHT-CLICK IT then wear it like a chestplate.
Fake-Herobrine wonders what he's wearing.
After that, use your electric tools. When they discharge, they will recharge with the energy from the bat-pack. You can track the bat-pack's charge by looking at the bar below it on your inventory, or if you're exclusively wearing the bat-pack, looking at the armor bar.
Energy Crystal
Energy Crystals are an advanced energy storage item (40000 vs. the RE battery's 10000 EU), made out of diamonds. They are crafted out of 8 redstone dust and 1 diamond (or industrial diamond). They start out uncharged when crafted.
They have the same properties as RE Batteries, except that they need to be charged in a Crystal Charger, and can only be used as battery in MFE Transmitters, MFS Units and Terraformers.