https://resource.heltec.cn/download/WiFi_Kit_32_V3/HTIT-WiFi%20kit32_V3(Rev1.1).pdf Lithium battery(≥250mA) min: 3.3 typical: 3.7 max: 4.2
So I guess I could try to run it on three AAA batteries. Worst thing to happen is I fry the board, which was only 10€. I'll wait for a reply here though
Edit: I meant AA batteries