Try picking up any IC2 fluid with a bucket, you'll just get a water bucket back. It's encouragement to use IC2 Cells or Universal Fluid Cells.
What would you suggest needing compatibility with IC2 Biogas? It isn't a common thing other mods have specific generators for.
It probably becomes a water bottle because there's no defined item for a biogas bottle.
As far as working only for IC2 machines, that's only partially true. The semifluid generator and fluid heat generator are the only ones that can use the biogas directly, but there are ways to convert IC2 power to RF for machines from Buildcraft, Forestry, Railcraft, etc. (as covered in this thread: Best option for EU to MJ? - even though it says to MJ, it turned out the poster really needed RF)
It probably becomes a water bottle because there's no defined item for a biogas bottle.
As far as working only for IC2 machines, that's only partially true. The semifluid generator and fluid heat generator are the only ones that can use the biogas directly, but there are ways to convert IC2 power to RF for machines from Buildcraft, Forestry, Railcraft, etc. (as covered in this thread: Best option for EU to MJ? - even though it says to MJ, it turned out the poster really needed RF)
I know you can convert EU to RF or any other energy. I have large amount of IC2 biogas so dont know how to get rid of it 
I will be happy if that IC2 biogas will burn in Gregtech gas turbine or in some similar machine, like methane.
IC2 biogas is really easy to make in large quantities, so it will be nice to have some more use for it.
You want to get rid of it?
Make a generator what is enough for your use and everything you voidpipe then you do not have a trouble.
Or use a big tank^^" I mean BedrockiumTanks store more then enough and they are cheap to make(depends how you make it) its mostly only cobblestone.
This minetweaker script should make biogas burn in gregtech turbines (keeping mind you'll get less total EU, this just saves you space and maybe lag vs whole fields of semifluids). I haven't actually tested it yet though.
import mods.gregtech.Fuels;
Fuels.addGasTurbineFuel(null, <IC2:fluidBiogas>, 32);I actually would love it if it were registered with some sort of RF engine (or with steam boilers, given that gregtech can already use normal everyday steam). Conversion via electrical engines is limited (only 20RF/t without losses), and I like having a single power source. Sadly Minetweaker's hooks don't get into any engines or dynamos right now (ignore the wiki saying combustion engines, buildcraft support was bugging out and minetweaker pulled it).
This minetweaker script should make biogas burn in gregtech turbines (keeping mind you'll get less total EU, this just saves you space and maybe lag vs whole fields of semifluids). I haven't actually tested it yet though.
Codeimport mods.gregtech.Fuels; Fuels.addGasTurbineFuel(null, , 32);
I actually would love it if it were registered with some sort of RF engine (or with steam boilers, given that gregtech can already use normal everyday steam). Conversion via electrical engines is limited (only 20RF/t without losses), and I like having a single power source. Sadly Minetweaker's hooks don't get into any engines or dynamos right now (ignore the wiki saying combustion engines, buildcraft support was bugging out and minetweaker pulled it).
that will be nice, if it works...
Biogas production setup is very cheap, with bigger generator it could be nice... Biogas = EU + heat + fertilizer
