How are the Curiosity rover's batteries doing after all these years (and all these cycles)? Have they degraded significantly?

Question

Curiosity has spent 2820 sols on Mars and this answer to About how long will Curiosity last on its nuclear power? points out that its batteries may wear out faster than its RTG.

Question: How are Curiosity's batteries doing after all these years? Have they significantly degraded? If so how does this impact its roving abilities?

Does the Curiosity rover really have a chance of driving to the top of Mt. Sharp?
At what incline would curiosity require twice the electrical power to drive compared to a flat grade?
Which wears out faster on RTGs; the R's or the TG's? (the radioisotopes or the thermocouples)
How much altitude will curiosity gain by its climb now from the clay-bearing unit to the sulfate-bearing unit?
About how long will Curiosity last on its nuclear power?

For Opportunity, before the end of communication (5111 sols), its main battery went through 5000 charging cycles and retained 85% capacity. — Mys_721tx, Jan 02 '21 at 00:43
@Mys_721tx I want one of those in my laptop right now! What? How heavy? Okay, in my backpack at least ;-) — uhoh, Jan 02 '21 at 00:46
@Mys_721tx Please consider posting that as an answer. You can add a sentence in the beginning that it's not about Curiosity, but it's a relevant (and impressive) benchmark since the evolution of rover technology at NASA is incremental. — uhoh, Jan 02 '21 at 00:48
There's a paper from 2017 with detailed graphs on Curiosity's (MSL's) batteries: "The use of lithium-ion batteries for JPL's Mars missions" (The actual paper has a graph with discharge capacity over time, but it's paywalled) — KarlKastor, Jan 02 '21 at 01:00
@KarlKastor that PDF is 50 slides long, can you mention which one cites the as-yet unnamed paper you're talking about? NASA may (or may not) host a publicly accessible copy somewhere: When will NASA PubSpace really make publicly available most of NASA funded research papers? In the mean time, I think there is enough in that PDF to write an answer here already! As each slide carries the NASA logo it should be okay to include screen shots from the PDF in an answer directly. — uhoh, Jan 02 '21 at 01:19
@uhoh As I said, the paper is called: "The use of lithium-ion batteries for JPL's Mars missions". I linked the presentation of that paper, because the paper itself is paywalled. Figure 10 in the paper is a very nice graph of discharge capacity over time. — KarlKastor, Jan 02 '21 at 01:24
@KarlKastor that kind of thing is very confusing! This is much clearer: "There's a paper from 2017 with detailed graphs on Curiosity's (MSL's) batteries: The use of lithium-ion batteries for JPL's Mars missions (cited/discussed/found here)" I don't think I'm the only person that assumes the text of a link is the title of the thing linked-to, and not a separate and independent piece of information needing to be parsed separately. — uhoh, Jan 02 '21 at 01:36
@CamilleGoudeseune sorry but this title I'm going to keep as-is; it conveys additional information and context that those who've had to replace an expensive battery in a piece of electronics can identify with. Have Curiosity rover's batteries degraded significantly? is so dispassionate about something so critical that I think it's easily overlooked. — uhoh, Jan 02 '21 at 06:19
@CamilleGoudeseune but please continue your edits, they are most welcome! — uhoh, Jan 02 '21 at 21:59

Mys_721tx · Accepted Answer · 2021-01-02T01:41:34.763

Although we have no direct report of how Curiosity's batteries are doing, we can use Opportunity's case as a reference as they are similar in many ways.

The Mars Exploration Rovers (MER, Opportunity and Spirit) and the Mars Science Laboratory (MSL, Curiosity) both use lithium ion batteries from Yardney. (1) The MER batteries are rated for at least 400 cycles at 40% depth of discharge. (2)

The MER batteries are designed to operate with 90% of initial capacities after 300 cycles at 50% DoD. (1) By the time Opportunity ceased communication, its batteries went through 5000 cycles and retained 85% capacity. (3) Both exceeded the original design requirements. Given the MSL batteries are designed to operate with two cycles each sol and total of 670 sols, (1) we should except a similar life on Curiosity.

Furthermore, the MSL battery capacity loss is about 1 Ah per 300 sols and the end of life capacity requirement is 59 Ah. (4, 1) A simple extrapolation shows 8100 sols from the initial 86 Ah.

How are the Curiosity rover's batteries doing after all these years (and all these cycles)? Have they degraded significantly?

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