Base on the question, and in my further computation, the possible answers would be the following and I hope you are satisfied with my answer and feel free to ask for more.
- If you want to determine the Thevenin equivalent voltage and resistance without overloading the battery, then apply some known resistance
<span><span>RL</span><span>RL</span></span> and measure the output voltage as <span><span>VL</span><span>VL</span></span>. Measure the voltage without a load as <span><span>V<span>OC</span></span><span>V<span>OC</span></span></span>. The voltage divider equation tells us that
<span><span><span>VL</span>=<span>V<span>OC</span></span><span><span>RL</span><span><span>R<span>TH</span></span>×<span>RL</span></span></span></span><span><span>VL</span>=<span>V<span>OC</span></span><span><span>RL</span><span><span>R<span>TH</span></span>×<span>RL</span></span></span></span></span>
Solve for <span><span>R<span>TH</span></span><span>R<span>TH</span></span></span>, and you know that <span><span><span>V<span>TH</span></span>=<span>V<span>OC</span></span></span><span><span>V<span>TH</span></span>=<span>V<span>OC</span></span></span></span>.
