Faced with the difficulty of finding my happiness in the trade, I bought a rechargeable 9V rechargeable battery (actually 8.4V) of 170mA and I dissected it.
It contains 7 NiMh 1.2V cells, just take 4 and you get a great mini battery of about 15 grams. It’s perfect for equipping a Fiu.
The photo above speaks for itself.