The title says it all. Now that Charlie has a Pi-4, I want to make sure he has enough battery life to run longer than 10-15 minutes at a time.
One thought is a Lithium battery pack, like the ones used on cordless drills. Unfortunately, 12v drill batteries are now very difficult to find. I can get the 18v One+ Ryobi batteries - and I have chargers for them - but I fear that attaching 18v to Charlie will leave a smoking hole in the carpet.
For the Pi4 Idle is 3.4 watts and my 8x Panasonic Eneloop Pro 2550mAh NiMH cells delivered about 23 watt-hours.
If you promise not to try machine learning while moving, you may be able to continue to use the eight-AA format, or perhaps try a 10 AA cell holder with the Eneloop Pro cells. (They cost a bunch initially, but because they deliver what they promise for twice the cycles of Chinese cells, the per hour cost ended up the same.)
Strongly suggest you create a load map e.g.:
Max startup battery current seen on meter: 430ma at 10.7v
Average idle battery current: 318mA (6/2019) at average 9.4v or 3 watts
Estimate Power Used in Test 22.3
Portion of Rated/Measured Battery Capacity Available 83%
Distance Sensor draws 30mA at 10.1v battery of Rated
Pan Servo draws 70-100mA at 10.1v battery
forward() “no-load” draws ~200mA extra (~430mA total) at 9.8v
forward() “loaded” draws ~330mA extra (~580mA total) at 9.5v
Connecting with remote desktop adds 10mA
Each “Eye” draws about 15mA at 9.5v
Speaking with espeak TTS draws about 8mA at 9.1v
Running glances draws ~40ma ave., 80ma peak, temp +3deg to 53C, (CPU at 5%)
Speaker (idle) draws ~1mA at 5v
GoPiGo3 PowerLED went “yellow” and quickly “Red” at around 7.4v?
My philosophy for Carl is to manage load to find limits and stay out of trouble. Perhaps, if you want to try really pounding a Pi4 get another one and put it on your desk. The GoPiGo3 board will not supply enough 5v to drive the Pi4 to the max, but will serve up enough for exploring lots of topics.
You can also just add a usb-c powerbank to the Pi4 power connector and use the existing batteries to power the GoPiGo3, no?
I really want to post a picture of Charlie connected to a 12v car battery with huge-honkin’ jumper-cables as a goof. Not really connected, but to make it look like I’m powering Charlie off a gigantic DieHard!