Thank you Bernhard,
your comment was quite useful. As mentioned in https://bugs.debian.org/873038 and https://bugs.debian.org/927163
a few changes were necessary to fix this issue:
diff --git a/config-4.19.0-10-amd64 b/config-4.19.0-10-amd64
index eb55c7b..c952314 100644
--- a/config-4.19.0-10-amd64
+++ b/config-4.19.0-10-amd64
@@ -3918,2 +3918,2 @@ CONFIG_I2C_SCMI=m
-CONFIG_I2C_DESIGNWARE_CORE=m
-CONFIG_I2C_DESIGNWARE_PLATFORM=m
+CONFIG_I2C_DESIGNWARE_CORE=y
+CONFIG_I2C_DESIGNWARE_PLATFORM=y
@@ -4460 +4460 @@ CONFIG_BCMA_DRIVER_PCI=y
-CONFIG_MFD_CORE=m
+CONFIG_MFD_CORE=y
@@ -4466,2 +4466,2 @@ CONFIG_MFD_CORE=m
-CONFIG_MFD_AXP20X=m
-CONFIG_MFD_AXP20X_I2C=m
+CONFIG_MFD_AXP20X=y
+CONFIG_MFD_AXP20X_I2C=y
@@ -7234 +7234 @@ CONFIG_MMA9553=m
-# CONFIG_AXP288_ADC is not set
+CONFIG_AXP288_ADC=m
After recompilation of the kernel the directory /sys/class/power_supply was populated and I got a battery indicator on the taskbar.