Or, how about one of these:https://www.pololu.com/product/3798https://www.pololu.com/product/3799
My probably last questions are, at what voltage shall I recharge the NiMH batteries? I have purchased following batteries:https://www.reichelt.de/nimh-akku-aa-mignon-2100-mah-1er-pack-xc-x2100aa-p190936.html?&trstct=pos_0In the datasheet, there are some plots with Chinese axis but it is clear what is shown (page 7 in the pdf):https://cdn-reichelt.de/documents/datenblatt/D500/XC_X2100AA_DB.pdfFully charged, the batteries hold a voltage of around 1.4V. For lower temperatures, that voltage exceeds even 1.5V.Looks to me like I can go for a charging voltage of 1.4V. What do you think?The solar panel should be placed outdoor to recharge the NiMH batteries over the whole year and power an MCU that records sensor values. I am not sure whether it will work to operate the NiMH battery and the charger in a temperature window of -10 to 50°C.