Wednesday, January 30, 2013

Death of a Battery | Do the Math

Death of a Battery | Do the Math

Now the Conundrum

Okay, so I have a bad cell in a battery. Maybe the situation is salvageable. Perhaps a “battery doctor” could bring the battery back to an operable state. I’ve seen prescriptions online for how to recover some functionality from a bad cell. You can’t expect original performance, I gather. But perhaps it is possible to turn an otherwise heavy block of junk into a useful battery again.
Let me say up front that I am not a battery expert. I may be carrying misconceptions that need to be cleared up. Please correct me if I have things messed up. It’s a safe bet that when I get through this failure episode, I’ll know more than I do now.
Whether or not battery repair is possible/effective, I judge it to be a near certainty that the revived battery would be poorly matched to its brethren. We have, in my 2×2 arrangement, a series problem and a parallel problem. In series, when one battery is in worse condition than its partner, it will sit at a lower voltage in both charging and discharging scenarios. It would seem, then, that the partner in better health gets a higher absorb state (or equalization) voltage, which has the effect of keeping that battery in relatively better condition than its lesser companion. So there is a self-reinforcement going on that I imagine will ultimately go unstable, producing another cliff-edge.  Perhaps this is also why single cells in a battery (stacked in series) drive off the cliff.
The parallel problem is that if one chain is weaker than the other chain, a similar phenomenon happens. The “good” chain gets higher current during charging, better conditioning that chain while in absorb state. And then we have the power swap issue after sunset, where the weaker battery drains energy from the better battery until the two are at a similar charge state.
I am not, therefore, convinced that I want to try and revive the defective battery, almost certainly leaving me with a mismatched condition. So what’s the conundrum? Just buy a new battery!
Firstly, a new battery paired with old Battery F would produce a series mismatch problem, and also a parallel mismatch problem—assuming C, D, and F are in similar shape. To avoid the series problem, I could buy two new batteries, but this seems an unfortunate waste of battery F. For all I know, Battery E is an anomaly and I can expect another several years out of the other batteries.  [It's this sort of thinking that often gets me labeled as an optimist, despite impressions you might have otherwise formed from the content of Do the Math.]
Secondly, even biting the bullet and buying two new batteries will leave me with a parallel mismatch and attendant problems.
So it seems like a really bum deal! Must I replace all batteries at once?
I suspect that I am missing something here, and a new battery in an otherwise old set may work itself out in some non-destructive way. I am still adapting to my reduced-capacity PV reality, and meanwhile needed a bloggable topic that I could cover quickly, even if the saga is incomplete. I still need to do some research, and perhaps comments will help set things straight.


I have written before about the disappointment inherent in batteries.  Now I have another personal example.  Just when I had decided that my batteries were in their prime, crash. In our forced migration from fossil fuels over the coming century, large scale implementations of solar and/or wind are likely to transpire only in connection to energy storage solutions.  With storage comes headaches, even for technologies as mature as lead-acid.  Batteries will fail, and seldom at convenient times.  I liken my recent experience to driving a car without a gas gauge.  How tolerable will this situation be to our demanding society?  Big adjustments ahead…
Note to readers: I will be taking a holiday break in my normal two-week cadence, so that I plan to be back on Jan. 8.

very good comments below,  various other battery chemistries, links,!

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