Hi @henrikho ,
Try [https://www.alibaba.com/product-detail/Rechargeable-lipo-401520-3-7V-100mah_62091374520.html?spm=a2700.galleryofferlist.0.0.76794436eYrKt8|this] one
The 601720 on your battery refers to the dimensions of the battery, 6.0mm H x 17mm W x 20mm L.
The convention with batteries is that the 1st two digits are the height of the battery in mm and there is a decimal point between the two digits which is not shown, the next two digits are the width in mm and the last two are the length in mm .
The battery in the above link will physically fit into the space and has the same capacity as the original battery. Because it is thinner you may have to pad out the compartment to prevent it moving about too much though.
Have you tried searching for ''(insert helicopter make and model number) battery'' as sometimes batteries are listed for the device and not by their specifications?