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Discussion Starter · #1 ·
Let’s say you were lucky enough to be able to inspect a module before you buy.
How would you evaluate it the field?
The list might include:
- Physical damage, particularly noting the condition of the fuse wires soldered to the cell tops.
- Voltage? I’m not sure I see much more usefulness than a snapshot from this.
- Use a “pack sniffer” or other device to get more info?
We’ll presume that the vendor won’t allow a timed load test.
How about other concerns?
- Any way to ID when it was built?
- Are there any modules to be avoided? There are different revisions to the circuit board that is commonly replaced by 057, EVTv, or other aftermarket bms boards. Are there modules that Don’t work with these?
Many thanks for your replies.
 

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Biggest risk: coolant leaked into the battery, this causes current leakage and is non recoverable.

how to detect (except visually): cells out of balance.

all cells from a good pack should be the same voltage withing a couple of mV

you can bring a SimpBMS to read out the modules quickly on site.
 

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Discussion Starter · #5 ·
You can tell nothing about a battery’s capacity by voltage alone. A Tesla cell can charge to 4.2V and still only have 50% capacity, or 100%, you can’t tell.
Only a load test will tell you. Tesla does this ($235) for their owners with battery issues: a timed load test to determine battery capacity.
You’d think this’d be a common test for someone selling used modules, but I didn’t find any. Some guys never even did a full charge test. They had them ready to sell, depleted down to 20% to make them safe to ship, never tested, no warranty. And they’re asking $1x00 a module for that? Crazy.
The power blackouts from the fires here in California have every warm body looking for Tesla modules for backups and maybe those guys don’t care so there’s no giveaways. As great as the Tesla modules are, buying salvage is a total crapshoot, even if you have the wreck in front of you (unless you can get the car to cough up it’s charging history). Tesla modules are not immune from age and chemistry. John61ct is absolutely correct.
 
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