Battery Contact Springs: Conical Coils, Flat Contacts, and Plating That Actually Conducts
Every battery-powered product lives or dies by a part that costs a few cents: the battery contact. Getting force, geometry, and plating right prevents the intermittent-power complaints that plague cheap devices.
The three families
- Conical coil springs — the negative terminal classic. Telescoping design gives long travel and low solid height; see our conical spring guide.
- Stamped flat contacts — positive terminals and dual-polarity clips, often combining locating features; made as stamped flat springs.
- Wire forms — bent-wire contacts where currents are low and geometry is awkward.
Electrical design rules
- Contact force: maintain at least 50–100 gf per contact point across battery tolerance and spring relaxation. Force, not area, breaks through surface films.
- Contact resistance: specify < 50 mΩ initial, and define the test condition (dry circuit if your electronics are low-voltage).
- Wipe: a little sliding on insertion cleans surfaces; design travel so contacts wipe.
Plating that works
| Stack | Use case |
|---|---|
| Ni 2–5 µm | Cost-driven consumer, dry environments |
| Ni + Au flash 0.05–0.1 µm | Standard for reliable products |
| Ni + Au 0.2–0.5 µm | Medical, high-humidity, low-voltage logic |
Music wire must be fully encapsulated by plating or it rusts; stainless (302/304) contacts trade some conductivity for corrosion safety and often skip heavy plating.
Sourcing notes
Battery springs are a classic Taiwan strength: high-speed coilers plus in-cluster plating. Typical programs run 10k–10M pieces/year with vibration-feed-ready packaging. Send battery type (AA, 18650, coin), circuit voltage, and environment through our RFQ form.
Frequently Asked Questions
Why do my battery contacts work initially and fail after months?
Usually relaxation (force drops below film-breaking threshold) or plating porosity letting corrosion creep. Raise design force margin and upgrade the plating stack.
Gold flash or thick gold?
Flash (0.05–0.1 µm) suffices when there is wipe and reasonable force. Go thicker for dry-circuit logic signals, high humidity, or when cycles are frequent.
Can one stamped part serve both battery polarities?
Yes — dual contacts with a bridge are common and cut assembly cost, but ensure creepage distance and correct polarity keying in the plastic.