{u]Assumption:: I'll be referencing a mechanic present in RP2. I'm aware this is IC2, but I am assuming that the mechanic is in forge, and not exclusively in RP2. Secondly, I know that by the time you are able to acquire this, tin will not be an issue at all.
Summary A cell that can not only carry a large amount of lava, but can be reused once empty.
Recipe: I've a number of possible recipes, but all are decidedly high end. One has a single iridium plate and tin cell(s). Another has 4 iridium ores or 4 iridium plates.
Usage: As one would use a normal cell. However, on each use on a lava source, the "iridium cell" would charge (like a battery or an electric tool). On placing into a geothermal generator, it would discharge its stock of lava until empty (like a stack of cells would normally). It would not disappear, but would simply be an like an empty battery ready to be recharged on the next lake of lava.
Capacity: Another property I'll leave to any implementer. It would need to be evenly divisible into the range of possible values for damage, but for the price I would hope it would be at least worth 64 lava sources.
Additional Possible Usage: When crafted with an empty bucket, it will fill that bucket and subtract a single 'charge' from the cell. Or, one could instead place both a bucket and the cell into a custom-built machine, but a machine for one purpose has been denied very often. This is the RP2 mechanic; used mostly with the saws, but similar is used for crafting drills and saws out of full batteries, so I'm assuming this is a forge thing.
Thanks for reading.