hi
Is there a module to charge a battery with ultra low current. I would have a voltage around 3v but the current is verry small. I suppose it is some energy harvesting technology but mostly those are for ultra low voltage, not current.
Post a link to the technical information on the battery and your device. Also define very small current.
And how can the forum know what you mean by that ?
Is 'ultra low current';
10mA
1mA.
1uA.
1pA.
?
battery of your choice, what ever works best/easiest
lets say 1uA
Hi,
This is to general a question.
What chemistry battery?
What capacity battery?
Charging at 1uA will not charge a battery at all, batteries are not 100% efficient.
The 1uA will get swallowed by the inefficiency of the charging process.
What is your ultimate aim of this thread?
Does it have anything to do with Arduino microcontrollers?
Can you please tell us your electronics, programming, arduino, hardware experience?
Thanks... Tom... 
I will let others solve your puzzle since you cannot define it or tell us where an Arduino is involved. Good Luck!