# Can someone explain these battery charge discharge charts?

I have these charts from Renogy 12V Deep Cycle AGM Battery 100AH datasheet.

Can somebody explain to me In the first chart: what does the F.V/Time column present? In the second graph: What does each different line present?

In the second graph: What does each different line [represent]?

Here is the explanation of the lines in the graph. For reference, I guess the graph in the question comes from this datasheet:

Using the circled numbers (1 - 3) on the original graph and the numbers which I added (4 - 9), here are the meanings:

1. It's difficult to see (try zooming in - there is a solid line just to the left of the text "100%") but that shows the solid lines refer to a battery which has had a 100% discharge (i.e. a discharge at 0.05C amps for 20 hours); dashed lines refer to a battery which has had a 50% discharge (i.e. a discharge of 0.05C amps for 10 hours).

2. The charging assumes a total charge voltage of 14.70 V, which is 2.45 V per cell. (It is 2.45 V i.e. the per cell voltage, which is shown on the graph.) The charging shown in the graph also assumes a charge current of 0.1C amps.

(The graph assumes you understand C ratings for batteries, and also understand the CC/CV charging method for lead-acid batteries e.g. this page on Battery University.)

3. Lead-acid battery voltages are temperature dependent. The graph assumes a temperature of 25 °C (77 °F).

4. This dashed line shows the expected rise in battery voltage when charging a 50% discharged battery with the conditions explain in point 2. At the point where the cell voltage reaches 2.45 V (notice how the line remains horizontal i.e. the voltage remains constant) the charging switches from CC to CV to maintain that voltage. Use the scale on the left of the graph labeled: "Battery Voltage (V) / Per Cell".

5. Same as 4 except assuming the starting point is a 100% discharged battery.

6. This shows the ratio of energy going in during charge vs. the energy released during discharge, with a 50% discharged battery. Notice that that a full charge always puts in a little over 100% of the energy which can be released. In other words, charging a battery takes more energy than the battery can then release - batteries are not 100% efficient. Use the scale on the left of the graph labeled: "Charge Quantity (%)".

7. Same as 6 except assuming the starting point is a 100% discharged battery.

8. This line shows the charge current, starting at 0.1 C amps (as stated in point 2) with a 50% discharged battery. The start of line 8 cannot be seen, as it is underneath line 9. Both start on the left side of the graph where I showed with the arrow. Notice how when the battery voltage reaches 2.45 V per cell, the charge current reduces and enters the constant voltage phase of charging (sometimes called the "topping charge"). Use the scale on the left of the graph labeled: "Charge Current (CA)".

9. Same as 8 except assuming the starting point is a 100% discharged battery.

In the first chart: what does the F.V/Time column [represent]?

Regarding the table in your question, I already explained how to interpret that type of table and the meaning of "F.V/Time" in my earlier answer to a similar question here:

CSB batteries Constant Current Discharge Characteristics

• 6 is (correctly) about charge, not about energy. I figure some electrons get to decompose water (later recombined, but those charges are lost). I'm convinced more of the energy losses show up as differences in voltage: discharge from ~2.1 V to 1.75 V (nominal cut-off for 20 h), charge from ~2 V to 2.45. Commented Feb 14, 2023 at 8:28