Extending Battery

[nglessner]

Some ideas that could possibly extend battery life substantially. Obviously these would have to be tested to see if real-world results would pan out.

• Increase resistance on your battery voltage divider, and/or use a n-channel FET to disconnect when not in use
• use an LDO like the RP9080 which has a very low quiescent current (~2uA)
• turn off the "high draw" EPD and NTC when in deep sleep. I don't know how much time is needed to get a reading from the NTC thermistor, but the EPD when "off" draws ~1uA. Might not be a good idea to turn off the NTC if it increases the awake time.

Using this battery life calculator and some back of napkin guesses at power draw with these changes, the results went from 11 days to 25 days with a 500mah battery.

Another small change that might save some PCB manufacturing costs - if you're not using the temp pin of the TP4056, you might as well go with the much cheaper/smaller 4057 that omits the thermal protection feature. That shouldn't change the battery life equation any though.

[ovidiu4]

All are great ideas! Unfortunately when I designed the PCB I really thought that 1mA current draw during sleep is really good 😁

Version 2 will take into account all of these.

Maybe even a programmable timer like the TPL5110 to just disconnect everything from the battery. I just haven't found one that can be programmed digitally, like through I2C, and not with a fixed resistor...