Creating accurate State of Charge (SoC) curve modelling.

# Feature
We want to model a proper space battery SoC charge/discharge curve depending on the provided-power/power consumption in a dt. We can create a simple battery model having typical Lithium ions SoC behaviour. The model can be used to improve #8.

## Desired Behavior / Functionality
* Modelling Lithium ions SoC behaviour (V almost independent of the SoC).
* Modelling proper SoC vs Energy provided/discharge.

## What Needs to Be Done
* Checking already available python packages/battery models
* Implementing battery charge/discharge models
* Integrate model in #8

## How Can It Be Tested
* TBD (it depends on the availability of previous sources)

Start by reviewing issue #8 and checking available Python battery-model packages, as requested in the issue. Define how the lithium-ion SoC charge/discharge behavior will be tested, then implement the model and integrate it with #8; done means both behaviors are represented and the integration has test coverage.

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