[Solved / Archived] Witty Pi4 L3V7 Not Switching to LiPo battery

How big is that battery, and what is the maximum current it can deliver? Even if the battery is indeed 3.7V, it is still possible that it could not deliver the required current and hence the boot failed.

@admin 
One battery model that I'm using is 2000mAh.  Model LP803465

You may need to guide me like I'm 4 years old. What you are asking me to provide makes sense but I do not know how to determine this.  I found some documentation that said the standard discharge is .2C 5A and fast discharge is .5C 5A. 

My knowledge of batteries ends around testing the voltage and estimating runtime from stated capacity of a battery.

I'm open to recommendations for batteries.  I have numerous use cases but I prefer to use flat battery types when possible.

Thanks

@wallaby246 You may find detailed explaination of battery's C-rating here https://batteryuniversity.com/article/bu-402-what-is-c-rate

I did a quick search of the battery LP803465, and its max discharge current is 2000mA (peak) or 1000mA (constant), which is 1C or 0.5C.

Since the battery is 3.7V and Witty Pi 4 L3V7 converts it to 5V, assume the DC/DC converter has 90% efficiency, and the current needed by Raspberry Pi is I. We can calculate the actual current needed from the battery:

I'=Vout*I/(0.9*Vin)=5*I/(0.9*3.7) ~= 1.5*I

That means in order to deliver 1A current to Raspberry Pi, your battery has to deliver 1.5A current. During the boot your Pi may need more current, so most probably your battery would have to deliver more than 2A current at boot, which is kind of difficult for a battery like LP803465.

Thank you for the replies.

I have also tried with the 3.7V  5000mAh batteries from some Pi Sugar kits and it's the same result.  The Pi Sugar HATs do not function well overall but I do know Pi4's and Zeroes do boot and/or run from the pi sugar battery packs just fine. 

I've observed that my pi zero W2  maxes out at around .65A at boot and runs continuously at approx .162A with my use case.  I assumed that the "UPS" capability would just need to supply the Wattage and maybe a little more when the power switches from the USB power to the battery.

@wallaby246 Your assumption is correct, however:

Raspberry Pi consumes more current during shutdown, and the value you read may not be the actual maximum value. The peak current may exist for very short moment and your meter may not catch it. It is always good to give more buffer.

Even if your LP803465 battery still meet its specification, that is still too tight for such use case. This battery's discharge C rate is rather low.

Just FYI, we used single 18650 LiPo battery in our laboratry for testing Witty Pi 4 L3V7, and it worked pretty well. According to this article, 18650 LiPo battery ususally has discharge rate 10C, much higher than LP803465's 1C or 0.5C.

@admin 
I finally received and tested the 18650 LiPo and the UPS function did work as advertised.
Good stuff.  I hope I can find a flat battery pack that has a similar C rate.

Thanks again for the help.