I have created a power supply which provides 5V and 15mA. My battery (3.7V,520mAh) doesn't charge because this current isn't strong enough,it starts charging from ~150mA - 200mA. But my application consumes 2mA in average. For my battery to accept the charge, I plan to use a shunt battery charger. Is it the good thing to do?
First, if someone is concerned about efficiency, a shunt regulator is not the most efficient dc to dc regulator.
Secondly, LI-ion batteries are not forgiving of design flaws in their chargers. To avoid major problems (fire and explosion) their charging profiles need to be carefully observed - Voltage, current, time, battery temperature...
Here's a reference to app notes and data sheets to get the full story. http://www.linear.com/search/search.php?q=li-ion+charger