First, if you don't have it, buy (or make) a shortcut plug like the one in photo.
You can use it to check...
Buy it where? You didn't provide any link to the place that sells them.
You also seem to be talking exclusively about the uCurrent even though we've also been discussing the Fluke 8845A. I wish to point that out for clarity, for those who later come and read through this thread.
As to testing nA currents on battery voltage alone, consider well that such is not practical in that you may need to test small currents when connected to a AC powered source at times. In other words, just as is the case with any handheld or desktop meter, there are times when we need to test circuits powered by batteries and times when we need to connect them tested to a wall socket because that's the environment in which they will be used.
Sorry, I didn't provide link, you are literally on the other side of the planet, so I thought you might be able to find something closer to where you live.
And no I didn't even mention uCurrent. I was talking in general about microvolt and nanovolt and microamperes and nanoamperes measurement with any instrument.
At those voltage and current levels, impedances are so high and measured signal is so low that parasitic emissions, static fields, magnetic fields, triboelectric and thermal effects are sometimes greater than signal you are trying to measure.
Here is the link to a good read..
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwisiuXE56DTAhWmIpoKHeVJDFoQFgg6MAA&url=http%3A%2F%2Fwww.tek.com%2Fdocument%2Fhandbook%2Flow-level-measurements-handbook&usg=AFQjCNGVEOdo-RW87qH4qowipnt8wWqH_A&sig2=eV4eDeg3TGedyhA5b0A9jgIt is the "Low measurement Handbook" by Keithley (says Tektronix but that's corporate crap), a very good overview of the low level measurements and common pitfalls..
As for shorting bars, you can also buy two of these from Pomona:
http://www.mouser.com/ProductDetail/Pomona/5165-2/?qs=%2fha2pyFaduiB6fjNcFfbfg0LjqdcPIiv05%252bYHAJJ%252b9E%3d&utm_source=octopart&utm_medium=aggregator&utm_campaign=565-5165-2&utm_content=PomonaThey are shorts, and can be used in more than one combination.... Including two or more of them connected together..
As for your question, yes, sometimes you need to measure with power grid powered equipment. And then you have complications... Additional filtering, shielding....
You should try to avoid it, if you can..
Hope that helps.
Regards,
Sinisa