#### LTC4015
About $10.84/unit on Mouser.
From the datasheet (17/78):
##### Low Power Sources
```
The input undervoltage current loop (UVCL) can be engaged
to help keep the input voltage from decreasing beyond a
minimum voltage when a resistive cable or power limited
supply such as a solar panel is providing input power to
the LTC4015. A maximum power point algorithm using this
control loop has been preprogrammed into the LTC4015
to maximize power extraction from solar panels and other
resistive sources.
```
##### Features
```
Use of the serial port is completely optional. Even without
use of the serial port, the LTC4015 is a fully functioning high
performance battery charger which is highly configurable
using external components and pin connections. Chem-
istry/algorithm, cell count, charge current, input current
regulation (ICL), VIN undervoltage regulation (UVCL),
maximum power point tracking (MPPT), and switching
charger frequency and compensation are all externally
configurable without using the serial port.
For applications requiring the LTC4015’s advanced digital
features, the serial port provides a means to use the Cou-
lomb counter, read status and ADC telemetry data from
the measurement system, monitor charger operation,
configure charger settings (e.g. charge voltage, charge
current, temperature response, etc), enable/disable/read/
clear alerts, activate low power ship mode, and enable/
disable the battery charger
```
##### Example Schematic
![[Pasted image 20250120085408.png]]
`Vin` at the top left,
Battery Pack at the bottom right,
System Load at the top right.
*A great question to ask at this point - What kind of load do I intend to connect the pack to for discharge? Phone charger? Boil water? LEDs?*
##### Example Schematic (With Values)
![[Pasted image 20250120090814.png]]
##### Charging Methods
|**Mode**|**Voltage Requirement**|**Current Requirement**|**Feasibility**|
|---|---|---|---|
|**Trickle Charging**|Sufficient (5V > 2.85V)|Insufficient (300 mA > 6 mA)|**Not Feasible**|
|**Normal Charging**|Sufficient (5V > 4.2V)|Insufficient (3.2 A > 6 mA)|**Not Feasible**|
|**Preconditioning**|Sufficient (5V > 2.85V)|Insufficient (300 mA > 8.8 mA)|**Not Feasible**|
|**Float Charging**|Sufficient (5V > 4.2V)|Sufficient (<10 mA < 6 mA)|**Feasible**|