Batterypack discharge

You have considered only the voltage rating of your battery pack. What is the Ah and C rating? Say if your battery pack is rated for 72V 4Ah with a C rating of 2. then it means your battery pack can only deliver a maximum of 8Amps (Ah rating * C rating) to your loads through BMS. Suppose if your load is drawing more current from the pack your battery voltage will collapse meaning it will drop to a very low value. 

When you remove the load no current will be drawn and hence the voltage will return back to normal. This problem gets worse when you are powring a motor, because you have to make sure your battery pack can provide enough starting current required by the motor, this starting current will normmaly be high than the operating current of the motor. 

Hi Peter! The issue you are facing is only based on the load you are connecting with your DIY battery. Try to check the battery current rating i.e., it Ah rating like commonly used DIY 18650 Cells are of current rating 2200mAh means that 2.2 A of current for 1 hour. Also check for the C rating of the battery cell. I think you are putting maximum load on the battery by using some kind of high current modules, motors which has high current in start. And also you said that when you disconnect the load from battery there seems that your battery is fully charged and displaying full voltage of the battery, it's known as no load voltage. Try to check the battery and as well as your load current rating, hope your issue will get solve after this. I would like to recommend you to contact the SSLA technical support team for getting better assistance in your project issues.

The purpose of a battery is to store energy and release it at a desired time. This section examines discharging under different C-rates and evaluates the depth of discharge to which a battery can safely go. The document also observes different discharge signatures and explores battery life under diverse loading patterns.

The electrochemical battery has the advantage over other energy storage devices in that the energy stays high during most of the charge and then drops rapidly as the charge depletes. The supercapacitor has a linear discharge, and compressed air and a flywheel storage device is the inverse of the battery by delivering the highest power at the beginning. Figures 1, 2 and 3 illustrate the simulated discharge characteristics of stored energy.

Hi Peter! The issue you are facing is only based on the load you are connecting with your DIY battery. Try to check the battery current rating i.e., its Ah rating like commonly used DIY 18650 Cells are of current rating 2200mAh means that 2.2 A of current for 1 hour. Also check for the C rating of the battery cell. I think you are putting maximum load on the battery by using some kind of high current modules, motors which have high current in start. And also you said that when you disconnect the load from the battery there seems that your battery is fully charged and displaying full voltage of the battery, it's known as no load voltage. Try to check the battery and as well as your load current rating, hope your issue will get solved after this. I would like to recommend you to contact the Sierra Software Ltd. technical support team for getting better assistance in your project issues.

A discharge/charge cycle is commonly understood as the full discharge of a charged battery with subsequent recharge, but this is not always the case. Batteries are seldom fully discharged, and manufacturers often use the 80 percent depth-of-discharge (DoD) formula to rate a battery.