ESP-32 data logger (2) --- 12V 7.2AH SLA battery (5) -- partial failure (UPDATED)

 I conducted a test of the ESP32 data logger (link), and simultaneously testing the LM317 charger circuit (link). 

Details: 

• The current limit on the LM317 circuit was set for 0.72 amps
• The charge voltage was set to 13.8 volts
• The battery was discharge to about 30% capacity 
• Charging was done over a 10 hour interval
• The logger was set for 1 measurement every 10 seconds
• Voltage sense was through ESP32 ADC0 using a 1:0.128 voltage divider (6.8K-1K).
• Current sense was through ESP32 ADC3 taken across the charger's 0.825 ohm, current sense resistor. 
• The ESP32 ADC channels were set at 12 bits, 0 to 3.3V
• Logged data was smoothed using Excel moving average filter, 20 samples wide. 

Logged charging curve is shown below: 

The charge current failed to reduce below 0.2 amps after 10 hours of charging.  I am not sure why.  I suspect the  battery has some leakage.  Will be checking this.

The  IR drop across the charger current sense resistor causes an error in the battery voltage measurement.  This is compensated in Excel by subtracting the voltage drop from the measured battery voltage. 

The measured current doesn't seem capable of going less than 0.17 amps.  I think this is a problem with the ESP32 ADC.  I'll need to investigate further.  It's a little disappointing. 

This task is to put the charger and logger circuit into separate enclosures. 

UPDATE:

1. For the logger circuit, it seems the ESP32 ADCs have a very evil reputation.  I am going to order  some ADS1115  4 channel 16 bit ADC modules, and try to improve the ADC accuracy.

2. For the charger, I am going to put away the LM317 charger for now and build a circuit around the UC3906 SLA battery charger chip.