Lipo batteries with arduino nano

[kodfghj]

Hi guys! Firstly I want to mention that I know very little about electronics and this is my first time trying to make something using arduinos.
I'm using arduino nano 33 ble rev2. My end product needs to be small, lightweight and wearable, so the initial idea was to power the arduino directly with a LiPo battery (no voltage converter). It technically should not have worked bc the battery I'm using is 3.7V while the input voltage for Vin should be at least 4.5V. It however did work, arduino was on and transmitting data.
Unfortunately, it did not last long. One day, after plugging in the battery, the board did not turn on and just started heating up instead. Now it doesn't turn on anymore, even if I use the USB to power it. Can anyone help me understand why it happened? And how do I avoid this in the future? Thank you in advance and sorry if this is a dumb question.

tldr: powered an arduino with 3.7v LiPo battery through Vin with 4.5v min voltage. Arduino worked fine initially, but one day started heating up and broke. not sure why

[LarryD]

• I believe Vin needs 5-18V.

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• Always show us a good schematic of your proposed circuit.

• Show us good images of your ‘actual’ wiring.

[sonofcy]

You will need two LiPo's in series. Apply the + lead to the VIN pin and the - lead to one of the G pins. An internal buck converter changes the 7.4V nominal you will be supplying to 3.3V.

As to why what happened happened, that is likely too long an explanation but it is expected.
Here is the power section of the NANO 33 BLE Rev 2