The BatPack, or battery backpack, is a wearable item from IndustrialCraft2 that can provide energy to certain electric tools. It stores up to 60,000 EU, which is essentially 6 times the storage of any individual tool or battery.
The BatPack can be used as a RE Battery or equipped in the Chest Slot. If equipped in the Chest Slot, it can provide power for any relevant tool:
Using a tool with BatPack energy available will charge the tool (up to twice per use) from the BatPack. In other words, if you take a halfway dead tool and begin using it with the BatPack, the tool's energy bar will eventually be full. When using a tool, the BatPack supplies the energy needed for that use, as well as charging the tool itself. It can be used in conjunction with a dead tool to instantly charge it, by destroying a block when the tool has no charge, this, however, may be a glitch. The BatPack breaks from a moderate amount of damage, but only when empty. It provides one and a half armor points.
Again just like an RE Battery, a batpack can be used to power machines.
The BatPack can be upgraded to the LapPack which stores 300,000 EU and can charge up many other tools. Please note that the BatPack cannot charge the Advanced Chainsaw, Advanced Diamond Drill, or any other Tier 2 tools. If you want to charge those on the go, upgrade your BatPack to a LapPack.
Alternatively it can be charged when worn by using the Static Boots or the Solar Helmet. They can be used in conjunction for greater charging, or replace each other when the charging requirements are not fulfilled.