Does a plastic battery case always need a flame-retardant grade?

Answer: No. Storage near charging points justifies OI above 27; dry stock can stay on copolymer at 2.8 mm.

Is a 3.5 mm wall safer?

Answer: No. Thick walls cool slowly, the shrinkage differential concentrates at the corners, and the part splits at the radius.

Certificate or sample for electrolyte resistance?

Answer: Both. The certificate identifies the grade, the sample the batch; a new supplier shifts mass change by 0.8 points.

How much regrind is acceptable?

Answer: Twenty percent at most, never in the base or bosses. Two heat histories cut notched impact, so that batch is re-qualified at 0.9 m drop.

Does colour affect flame retardancy?

Answer: Yes. Carbon black helps char; excess titanium dioxide in pale colours pulls oxygen index down by 1 to 2 units.

How to Choose a Plastic Battery Case: Five Checkpoints

Quick answer: Choose the resin before the shape. A plastic battery case is settled by five numbers — oxygen index, 24-hour electrolyte mass change, wall at the rib root, melt window and batch retention — and only afterwards by price.

Five checkpoints for a plastic battery case
Checkpoint one: resin grade and flame retardancy
Checkpoint two: electrolyte resistance in three readings
Checkpoint three: wall thickness and rib layout
Checkpoints four and five: moulding window and batch release
FAQ

1. Five checkpoints for a plastic battery case

Two suppliers can quote the same 520 × 380 × 220 mm outline 18 RMB apart; the difference sits in the wall, not the drawing.

Run them in order: resin and flame retardancy, electrolyte resistance, wall thickness, moulding window, batch release.

Checkpoint	Ask for	Pass value	Failure sign
Resin and flame retardancy	Base grade, oxygen index	Flame-retardant PP, OI above 27	Burns on, drips ignite cotton
Electrolyte resistance	Mass and tensile after soak	24 h change ≤1.5%	Whitening, lifted edges
Wall thickness	Side, base, lid, rib root	Side 2.2 to 2.8 mm	Bulges under a stack
Moulding window	Melt, mould, cycle	215 to 230 °C, 55 s	Sink marks, split weld lines

2. Checkpoint one: resin grade and flame retardancy

Copolymer PP is the usual base for a plastic battery case, with flame retardancy from the additive package. Brominated systems are efficient but raise migration questions; halogen-free grades give lower smoke at about ten percent less notched impact, recovered by 0.2 mm of wall.

Plastic battery case: dark grey shell opened flat, black foam in the lid, die-cut trays holding a camera, coiled yellow tape and a silver pen

Oxygen index exposes a weak compound before UL94 does: below 22 it burns on under a sustained flame, above 26 self-extinction becomes realistic. Five bars, median value, GB/T 2406.

UL94 must be read at thickness: a grade reaching V-0 at 3.0 mm may only reach V-2 at 1.5 mm, and this wall sits at 2.2 to 2.8 mm, so bars must match the thinnest wall.

3. Checkpoint two: electrolyte resistance in three readings

For a plastic battery case, soak a 100 × 100 × 2 mm plaque in 1 mol/L LiPF6 carbonate electrolyte at 23 °C for 24 hours, wipe, rest an hour, weigh. Pass means under 1.5 percent mass change, over 85 percent tensile retention and no whitening — all three at once.

Lead-acid work adds 30 percent sulphuric acid at 1.28 g/cm³ for 72 hours; PP handles acid better, so the soak rarely limits the choice. Weak points are the gasket and the metal insert, where five percent swell pushes a latch out.

Give liquid somewhere to go: a 1.5 mm lip per compartment, an 8 mm sump at the bottom corners, a 3 mm dam between rows.

4. Checkpoint three: wall thickness and rib layout

Thicker is not safer for a plastic battery case. Below 2.0 mm the side bulges past 4 mm after 350 kg stands on it for a day; above 3.5 mm the shrinkage differential moves to the corners. 2.2 to 2.8 mm side, 3.0 mm base and 2.4 mm lid is the band a mould holds.

Plastic battery case: macro of a black corner, narrow gasket groove and compression line on the curve, fine grained skin, recessed panel

Location	Target	Floor	Measure with
Side wall	2.2 to 2.8 mm	2.0 mm	Ultrasonic, 5 points per face
Base	3.0 mm	2.6 mm	Centre plus 4 corners
Lid	2.4 mm	2.2 mm	9 points across the top
Rib root	1.5 mm	1.2 mm	Sectioned sample

Vertical ribs at 45 mm pitch, 0.6 of the wall thick, 1.5 mm root radius; keep the spread between ultrasonic points under 0.4 mm.

5. Checkpoints four and five: moulding window and batch release

Melt 215 to 230 °C, mould 45 °C plus or minus 3, packing 35 MPa, cooling 25 s, cycle 55 s. A 650-tonne clamp with a 65 mm screw covers the 520 × 380 × 220 mm plastic battery case; an 800-tonne machine only adds flash risk.

Release runs in three steps: dimensional report on the first shot, one part weighed every two hours (4.2 kg, plus or minus 1.5 percent), three retention samples per batch. Drop is 1.2 m onto six faces after four hours at minus 20 °C; salt spray, 480 hours neutral, covers inserts only.

Conclusion

Two plastic battery case designs look identical on a pallet and behave nothing alike: the difference lives in the compound, in 2.2 to 2.8 mm of wall, in three readings after a soak. Settle the material first, and the plastic battery case that arrives will survive electrolyte, cold and stacking.

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.