Programs are accelerating, heat loads are climbing, budgets are squeezed. If your battery cooling choice is fuzzy, you invite overheating, power derating, and rework. This piece gives you a one-sentence rule of thumb and a decision path you can put to work immediately.
We’ll move in four steps: cell format → platform evolution → porting & distribution → risk & validation, then close with hybrids and how XD THERMAL delivers.
In the engineering practice, the way the cooling surface couples to the battery is governed first by cell geometry and packing density. Before arguing about processes, get the contact area and path length right.
Prismatic/pouch: favor large, flat contact and uniform heat spreading. Cold plates dominate because they deliver a controllable, highly repeatable thermal interface that can double as a structural element.
Cylindrical: rely on line-to-surface contact across rows. Serpentine tubes can be placed close to the cell columns and paralleled along the rows to equalize flow and temperature. The geometry itself nudges you toward this choice.
Cold plates disperse thermal resistance across a larger area and integrate smoothly with module/tray structures. They accept stiffeners, insulation coatings, and sealed sub-assemblies without drama.
Serpentine tubes excel where cylindrical arrays need near-cell cooling with layout flexibility and low changeover cost. You can mix the two, but designate a primary and secondary solution; otherwise your test matrix explodes and your BOM gains weight you never budgeted.
As Tesla moved from C2M to C2P/structural packs, cooling also changed. Instead of using short parallel channels inside modules, the system moved to larger pack-level channels with wider contact areas. The same basic rules apply everywhere—tube length, flow balance, and where ports are placed—and these are the same factors XD THERMAL focuses on when designing cooling for cylindrical cells.
With 18650/2170, many programs arranged tubing by module, in short parallel runs—easy to assemble, easy to service, and reasonably uniform. With 4680 and structural ambitions, larger cells and higher surface power density push cooling designs toward wider-area contact and more carefully managed flow. Testing now isn’t just about keeping each module even. It’s about making sure the whole pack stays at a steady temperature, even under crash loads, NVH, and the stresses of a full lifecycle.
In the early days, designers put the inlet and outlet on opposite sides. It looked neat, but the coolant lingered too long in some spots and the temperature spread crept along the line. Over time, the industry — Tesla’s C2P work included — shifted to putting both ports on the same side. That simple U-shaped layout made the loops shorter, the plumbing tidier, and the temperatures more even.
At XD THERMAL we’ve taken the same route, though with a more structured process. We run design-for-manufacture checks alongside CFD simulations, build trial parts with opposite- and same-side ports, and then bench-test them under different flow and pressure settings with calibrated restrictors. Where stubborn hot spots remain, we add small plate-style inserts or local flow diverters — without dragging the pump away from its efficient range.
The end result lines up with the best of today’s C2P designs: steadier cell temperatures, cleaner manifolds, fewer high-stress bends, and test data sets ready for DV, PV and PPAP.
Not all serpentine implementations are equal. Reusing a C2M pattern in a C2P context can magnify temperature and reliability issues.
C2M: You can use either straight parallel runs or bent serpentine paths, because there are fewer cells per loop and shorter paths; the thermal window for uniformity is wider.
C2P:prefer same-side ports + a U-shaped single-tube loop or straight parallel runs. Same-side topology cuts dead plumbing, improves flow balance, and tightens temperature uniformity; opposite-side layouts over long strings amplify inlet-cold / outlet-hot gradients.
Why does same-side + U-loop win in C2P?
1. Compact plumbing: Putting the inlet and outlet next to each other keeps the pipework short and the manifolds neat, which makes flow balancing simpler.
2. Keeping temperatures in check: A U-shaped return runs the supply and return lines side by side, letting heat even out locally and helping the whole system stay flatter in temperature.
3. Build and reliability: Fewer long runs mean fewer far-off joints to worry about, stronger pressure-holding performance, and easier tracking during assembly.
Practical tip: For C2P designs, begin with straight parallel runs or same-side U-loops. If you can’t avoid routing across the pack, use manifolds or orifices to balance the flow, and set strict limits on temperature spread and pressure drop.
For battery packs using prismatic or pouch cells, cold plates are usually the easier option. They give you plenty of contact area, add some structural support, and make the testing and sign-off process more straightforward.
A cold plate is basically a broad, flat surface with channels inside, sometimes with fins to guide the flow. That design spreads heat evenly, keeps pressure drop predictable, and follows a well-defined sealing and durability routine — which suits IATF-driven programmes and OEM testing schedules nicely.
Begin with a combined thermal, fluid and structural analysis to decide on the channel size and fin density. Design around your temperature targets and pressure limits, then pick the right manufacturing method — vacuum brazing, continuous brazing, friction stir welding, cold metal transfer, or a mix — depending on cost and production volume.
Validation then covers proof-pressure and leak tests, plus thermal cycling, vibration and impact checks. A cold plate can also double up as part of the tray’s load-bearing structure, helping cut down the number of parts and interfaces.
CATL (Contemporary Amperex Technology) Reference
CTP 3.0 “Qilin (Kirin)” places cooling elements between adjacent cells, creating large-area heat exchange. Public materials describe 4× heat-transfer area, halved temperature-control time, and support for rapid thermal start-up (~5 minutes) and fast charging (~10 minutes). Fundamentally, this is a plate/laminar cooling thought-world that validates large-area coupling for prismatic/pouch systems at high power.
ESS Liquid-Cooling: In stationary storage (e.g., EnerOne family), CATL uses integrated liquid cooling with CTP packaging and modular manifolds, emphasizing system-level ΔT control and lifecycle reliability.
C2P succeeds or fails on manifold design and branch discipline. Get the ports and distribution right, and the rest behaves.
Where the layout allows, put the inlet and outlet on the same side and run each branch in a U-shape. Size the headers properly so the flow stays even, and use calibrated orifices or restrictors to fine-tune each branch. Aim to keep the temperature rise from inlet to outlet within about 3 °C per branch (often tighter), and hold the flow variation between parallel paths to within 5–8%.
Start with cell format. In C2P, use straight parallel and same-side U-path. Prismatic/pouch → cold plates. Validate early; use hybrids to lock risk before scale.
Before arguing “tubes versus plates,” pin risk to measured KPIs. Otherwise, it’s all feelings.
Core KPIs：
● ΔT (intra-row/whole-pack)
● Pressure drop (pump power)
● Leakage rate
● Post-thermal shock failure rate
● Burst/hold times
● NVH and vibration life
● Environmental envelope (−30–60 °C)
● Thermal margin under fast-charge
During samples, map a 3-variable matrix of pressure–flow–temperature that covers peak and nominal points. Overlay fast-charge and high-C discharge on thermal cycling. For C2P programs, institute a hard gate on inlet-outlet ΔT per string; if you cross the redline, roll back to shorter branches or stricter straight-run parallelism before burning more time.
Platform migration doesn’t happen overnight. Hybrids are often the engineering-right answer.
When a cylindrical platform heads toward C2P, use a main straight-run tube network plus local micro-plates or a manifold distribution plate at hot spots. On prismatic platforms, layer a secondary liquid path or graphite thermal film around peaks. The aim is to lock down 80% of risk early while you refine the last 20%.
Keep the validation scope under control: first lock down the main flow consistency, then check what the side routes really add. Make sure the bill of materials IDs and process records stay tidy, so the setup can be repeated in mass production. And avoid changing too many things at once — otherwise tests turn into a black box, wasting time and hiding the real cause-and-effect.
Selection is only step one. Affordability, stability, and speed complete the commercial loop.
XD THERMAL provides a full-service supplier (FSS) model from co-design → samples → validation → mass production. We run in-house extrusion, a machining center, and an insulation coating line. Our operations follow IATF 16949, we typically accelerate development by ~30%, and we leverage 300+ delivered battery-cooling cases from EV and ESS. Across three plants (>100,000 m²), our annual capacity exceeds 1,489,200 units.
Highlights:
Design: co-DFM and thermal routing simulation, with comparative “straight-through vs. hybrid” packages.
Prototyping: fast tooling and pilot runs; first-article tested for burst, leak, and thermal cycle.
Validation: DV/PV/PPAP aligned, with repeatable KPI experiments.
Mass production: flexible switching across vacuum brazing, continuous brazing, FSW, and CMT; full traceability.
Start with cell format. In C2P, use straight parallel and same-side U-path. Prismatic/pouch → cold plates. Validate early; use hybrids to lock risk before scale.
