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Discussion Starter · #1 ·
Hi everyone,

So I had previously done some reading about the use of (smaller) batteries in parallel and in series. At a high level, it sounded like you could chain multiple different batteries in series and add together their voltage, but they would be current-limited (or would only work up to the lowest max current).

Given the price hikes on the Model S battery modules (my planned budget is up $10k since January just on batteries alone because of the increases), I was evaluating the possibility of mixing in other batteries to replace some of these and cut down on planned costs (without utterly sacrificing power and range drastically, like abandoning them entirely). One thought I had (if I could make them fit dimensionally) was to replace 3-4 Model S batteries with one of the bars from a Model 3. Based on what I've read, that would be about the same voltage and (in a 16-pack of the Model S) be an equivalent trade.

Has anyone tried chaining different batteries together before? Can the current draw be controlled?

Thank you!
 

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No for high C-rate usage all the cells in a given serial string must match, really should be the same factory run and state of health.

Not so strictly, strings compared across the parallel connection, but usually parallel is joined first.

The batteries is not a place to try to save money, unless it's a throwaway learning project.

Can (should?) be at least 20-30% of the overall cost, on a low end build, say under 25K USD
 

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Discussion Starter · #3 ·
This is not going to be a low end build, but I wasn't exaggerating the price increase. They could be purchased for about $1k per unit around here earlier this year, but now it's $1.5k unless I can get an intact pack and safely dismantle it (hard ask) for less. As of now, the batteries alone will be at least $24-25k. But cost wasn't the main driver for this; my ideal donor vehicle will have been an FR configuration, and I've seen (such as on the recent Mustang conversion posted here) that there can be sufficient space in the transmission tunnel to fit certain battery boxes. Given the small profile and long depth of the model 3 batteries, that seemed like a plausible use for the space.

Doubling back, when you say high C-Rate, how high did you mean?
 

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... my ideal donor vehicle will have been an FR configuration, and I've seen (such as on the recent Mustang conversion posted here) that there can be sufficient space in the transmission tunnel to fit certain battery boxes. Given the small profile and long depth of the model 3 batteries, that seemed like a plausible use for the space.
Each Tesla Model 3 module is almost one quarter of the width of the car's floor; that's much too wide to fit in any reasonable tunnel. Almost every non-Tesla module is a better fit.
 

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Model S module prices went up??. It's not like people stopped crashing these things...Don't count out the Leaf modules. They're much cheaper and pretty damn good if you have the space.

Electric GT also started putting together their own packs, and they're comparable in price and spec to Model S batteries, though they are unproven in the real world:

 

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Discussion Starter · #8 ·
Regarding different cells; I saw that other thread discussing battery options and it seems that only Tesla and Electric GT modules really compete in terms of Ah/kg (at least now that the LG Chem boxes are C&D'd). Saw someone had placed an order for the EGTs so waiting to see how those shape up.

Another option might be the recently (today?) announced Chevy electric crate system for next year (Chevrolet readies an electric crate motor for homebuilt EV hotrods) but they're still a little light on the full details, and that will require dismantling the battery pack to fit the cavity space available.

But back to the main focus: It sounds like all batteries in series need to be the same voltage and amperage and amp-hours to work? I guess there was a reason we only covered networks of resistors in Intro to Circuits. But that does simplify the planning and design process, I guess. Thanks for the responses/feedback!
 
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