Why does a battery case need swell allowance?

Answer: Modules grow about 3 percent near full charge, which is 6 mm on a 200 mm stack. An 8 mm gap covers it.

Is thicker insulation always better?

Answer: No. Past 5 mm assembly compression eats the gain while cost doubles; 3 mm aerogel with a 15 mm air gap is the practical point.

Why not point the vent upward?

Answer: Rain collects in an upward port and a wet membrane loses airflow. Thirty degrees above horizontal with a splash lip keeps it breathing.

Do three-high stacks need steel straps?

Answer: Only when going higher. Three high at 400 kg per unit holds with film, while four high puts 1200 kg on the bottom and needs straps plus 32 mm feet.

Is IP67 safer for a battery case?

Answer: A battery case has to breathe. Cycling builds a pressure difference, and a blocked valve pushes the gasket open, so IP55 with a breather is steadier.

Battery Case Selection: Five Criteria

Quick answer: A battery case is specified in one order: cavity, insulation, venting, stacking, sealing. The first two fix dimensions and the rest follow.

Five Criteria for a Battery Case
Cavity Size from Module Outline
Insulation Thickness and Back Plate Rise
Vent Area and Opening Pressure
Stacking Load and Fork Pockets
FAQ

1. Five Criteria for a Battery Case

Order matters. Measure the module outline to fix the cavity, size insulation by the allowed temperature rise, set vent area by capacity, pick stacking by warehouse height, and leave sealing for last. Reverse two steps and a small saving becomes a new tool. Cavity and stacking are hard limits; insulation, venting and sealing trade off against each other.

Criterion	Typical value	Failure mode
Cavity	800 x 600 x 350 mm	Lid will not close
Insulation	3 mm aerogel, 15 mm gap	Back plate overheats
Vent	1.6 sq cm per kWh	Gasket pushed open
Stacking	Three high, 25 mm feet	Bottom unit collapses

2. Cavity Size from Module Outline

Cavity follows the module outline, not the cell count. Twelve 590 x 390 x 200 mm modules in three columns of four, 8 mm apart with 8 mm at each end, give 800 mm length and 600 mm depth; a 250 mm base holds them, 100 mm in the lid carries busbars.

Battery case: red shell open, ribbed flat lid, foam cut-outs with a red-wrapped pack, folded grey sleeve, screen unit and cylinder, two front latches

Modules swell about 3 percent, which is 6 mm across a 200 mm stack, so 8 mm covers the growth and still leaves finger room. Height is where drawings fail: add base, module, terminal, harness and lid, or the terminals press the lid ribs and the insulation gets shaved.

3. Insulation Thickness and Back Plate Rise

Insulation slows propagation rather than blocking it. Aerogel at 0.020 W/mK in 3 mm plus a 15 mm air gap beats 10 mm of plain foam at similar cost.

Write the acceptance test as a number: 300 C flame on one face for 30 minutes, back plate rise under 40 K.

Build	Thickness	Rise
Aerogel	3+15 mm	32 K
Ceramic fibre	6 mm	45 K
Plain EVA	10 mm	70 K

Thermal bridges matter more than thickness: a 1.5 mm steel wall carries heat past the aerogel, so wrap the divider 20 mm and add a 2 mm pad.

4. Vent Area and Opening Pressure

The tighter the battery case, the more it needs a controlled vent path: gas generation outruns what a gasket can leak, and pressure finds the thinnest seam.

Battery case: black shell corner close-up, rounded edge and pale seal line, foam cut in a circle around one round black module

Size the vent by capacity at 1.6 sq cm per kWh, so a 5 kWh module needs 8 sq cm, which is two 22 mm valves. Set opening pressure at 8 kPa: below 6 kPa valves chatter on the road, above 12 kPa the shell deforms first. Angle the port 30 degrees above horizontal with a splash lip, channel 1.2 times the port area.

5. Stacking Load and Fork Pockets

Stacking is the most underrated item. Three units high at 400 kg each means the bottom one carries 800 kg, which sets rib density, foot area and lid stiffness.

Feet go to 25 mm minimum, fork pockets to 120 x 45 mm at 60 mm above the floor with a 3 mm flange, or the fork tips crack the edge. A 6 mm locating groove with 2 mm clearance stops lateral shift, and hardware should run 480 hours of salt spray before a coastal warehouse whitens it.

Stack	Load per unit	Bottom load	Feet	Fixing
Two high	400 kg	400 kg	20 mm	Two wraps of film
Three high	400 kg	800 kg	25 mm	Film plus corners
Four high	400 kg	1200 kg	32 mm	Steel straps, four points

Conclusion

Five criteria come down to three acts: size the cavity from the module outline plus allowance, pair insulation with venting, and fix stacking and feet by warehouse height. A wrong cavity means a new tool, a mismatched insulation and vent pair shows up in an abnormal event, and a wrong stack fails at the first merge of stores. Get all three into the drawing and the battery case is chosen correctly.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.