Charge lithium ion batteries at -30°C
Yes, you will damage the battery if you charge at low temperatures (beyond the product specification). You can read this if you only believe research papers: https://www.researchgate.net/publication/282407632_Optimal_Low_Temperature_Charging_of_Lithium-ion_Batteries

If you are using solar to charge the battery, then of course you could use solar power to heat the battery. It makes your charging design a little more complex but it would not appear ridiculously so.