# BATTERY
* 1S LiIon/LiPo (3.7 V nominal)
* 18650 for easy ubiquitous availability (~3,000 mAh each)
* connect cells in parallel until we get the capacity we want
* lipo can charge at 1C

## CELLS
[INR18650-35E](https://lygte-info.dk/review/batteries2012/Samsung%20INR18650-35E%203500mAh%20%28Pink%29%20UK.html)


# POWER BOARD
[Adafruit 6091](https://www.adafruit.com/product/6091)
* $7
* 5-18V input, USB-C or PV/DC
* CC at 1.0 A, 0.5 A, or 0.25 A
* handles LiPo/LiIon or LiFePo cells
* optional thermistor to reduce charge current when battery overheats
* battery under voltage protection disconnects the battery from the load at 3 V
* [schematic](https://learn.adafruit.com/adafruit-bq25185-usb-dc-solar-lithium-ion-polymer-charger/downloads#schematic-and-fab-print-3188140)

Max charge rate is 1 A at 3.7 V nominal battery voltage, which is 3.7 W.


# PHOTOVOLTAIC PANEL

Anything 5-18 V should be fine, the charger can't use more than 3.7 W.

Trying this one: <https://www.amazon.com/Soshine-6w-Performance-Monocrystalline-Cellphone/dp/B09ZL3F7CT?th=1>


# ALTERNATIVE POWER BOARDS

## CHARGERS
1. [5V 2A USB-C](https://www.amazon.com/DWEII-Converter-Step-Up-Charging-Protection/dp/B09YD5C9QC/)
2. [5V 2A](https://www.amazon.com/Ruiwaer-Discharge-Integrated-Adjustable-Charging/dp/B08QHVW5J8)
    * have on hand (i think)
3. [Adjustable](https://www.amazon.com/Lithium-Battery-Charger-Charging-Converter/dp/B089NG9TFW)
    * combine with [heatsink](https://www.amazon.com/Printer-Heatsink-Thermal-Conductive-Adhesive/dp/B07RKHRHJV)

strawman: charging up to 4v with the INR18650 (see `CELLS:INR18650-35E` for the discharge capacity graph, and `CHARGERS:3` for 4V cutoff w/ a 5V panel) gives us ~3000mAh, or 88% of the 3398mAh tested battery life.

## BMS
2. [3S 60A](https://www.amazon.com/dp/B0B9MMZWXC)

# SOLAR
* mppt charge controllers:
1. <https://www.amazon.com/Waveshare-Solar-Power-Manager-Regulated/dp/B0CT2ZBML9>
2. <https://www.amazon.com/4-4-6-5V-Lithium-Battery-Charger-Controller/dp/B08DY28BXW>