Brownout detector was triggered when wake up from deep sleep on batteries

[schejbity]

Board: LILYGO® TTGO T-SIM A7670E R2 without GPS Board version: 1.2

I need to power the board using batteries. I don't use the battery holder that is on the board, but on the + - contacts I soldered the wires that connect my battery pack with 4x18650 cells. I don't use the solar panel input.

I use the deep sleep functionality in the code. Wakeup is either timer based or via GPIO. The problem is that almost every time it wakes up, it resets, see the console listing.

I disconnected everything from the board except the battery pack and the problem still persists. So the problem is probably somewhere on the board. Do you have any ideas how this could be solved?

rst:0x5 (DEEPSLEEP_RESET),boot:0x12 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:2
load:0x3fff0030,len:1184
load:0x40078000,len:13192
load:0x40080400,len:3028
entry 0x400805e4

Brownout detector was triggered

ets Jul 29 2019 12:21:46

rst:0xc (SW_CPU_RESET),boot:0x12 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:2
load:0x3fff0030,len:1184
load:0x40078000,len:13192
load:0x40080400,len:3028
entry 0x400805e4
========================================
Wakeup was not caused by deep sleep: 0
Boot number: 1
========================================
Setup ESP32 to sleep for every 120 Seconds

Wait...
[14694] Initializing modem...
[14694] ### TinyGSM Version: 0.11.5
[14694] ### TinyGSM Compiled Module:  TinyGsmClientSIM7600
[14708] ### Modem: A7670E-LASE
[14708] ### Modem: A7670E-LASE
[14847] Initializing modem...
[19853] ### TinyGSM Version: 0.11.5
[19853] ### TinyGSM Compiled Module:  TinyGsmClientSIM7600
[21853] ### Unhandled: *ATREADY: 1
[21966] ### Modem: A7670E-LASE
[21966] ### Modem: A7670E-LASE
[23107] ### Unhandled: +CME ERROR: SIM failure
[25249] ### Modem: A7670E-LASE
...

[DevinCarpenter]

From everything I see, this is a low-voltage warning that is occurring as per this Have you checked that your battery pack voltage is stable under load? Do you have a proper BMS that you've bought or made? Have you tried this with another board using the 18650 battery slot on the back to make sure that it is not a problem with your code or your existing board? Any other ways you've tried isolating the problem?