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Tesla battery module buying guide?

1025 Views 3 Replies 2 Participants Last post by  john61ct
I was warned to be very careful when buying Tesla modules, especially from a salvage yard. I was told by the time the wrecked car works thru insurance and the auto auction, the battery could be fully dead.

Is the a buyers guide for purchasing Tesla modules or other used EV modules?

Thoughts:

Miles on car
Module voltage
Cell group voltages
Variance across all cell groups
Other tests?

Can a seller spoof the buyer by charging up a dead pack?
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Good voltage means almost nothing, but all groups close to identical on an untouched pack would be a good sign

unless as you say the seller produced that result.

Holding voltage during a CC load capacity test over several hours is a solid indicator, go from 100% Full spec, down to say 3.0V per cell-group, precisely timed.

But the remaining capacity compared to the original rating when new is the canonical one, State of Health SoH%

A 10-hour rate (0.1C) would get you much closer to nameplate, anything within say 80% would be a good result.

Doing it faster, say in under an hour at 1C, would show much lower total Ah, but if the voltage holds strong through most of it, say over 3.6Vpc that would at least eliminate the bad modules.

Internal resistance is also valuable but much trickier to standardise conditions, best used to comparison measure say every 50 or 100 cycles.
 
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