BMW i3 Battery Mount Bolt Replacement: Cost – Why $12 Bolts Can Trigger a $1,200 Mistake (And How to Get It Right the First Time)
“I dropped one of the rear battery mount bolts while swapping my i3’s pack. The local dealer quoted $420 for ‘subframe realignment and torque calibration’ just to replace four M10 bolts. I ordered OEM-spec replacements online for $11.80, used a calibrated wrench, and torqued them to 50 Nm + 90° angle—exactly per BMW TIS. Zero issues. Two years later, still rock-solid.”
You’re installing a new or replacement battery in your i3.
One bolt strips. Another snaps from corrosion.
Or maybe you’re reassembling after a repair—and realize you’re missing the exact fasteners.
Now you face a dilemma:
“Do I use generic hardware… or pay dealer markup for tiny pieces of metal?”
The wrong choice risks more than noise—it can compromise structural integrity, crash safety, and even high-voltage clearance.
In this guide, you’ll discover:
- The exact part numbers and specs for all i3 battery mount bolts
- Why material grade and coating matter (hint: stainless isn’t always better)
- Real-world replacement costs—from DIY to dealer
- How CNS BATTERY includes correct hardware with every pack
- And the one torque spec mistake that causes 80% of post-install rattles
Because in EVs, even the smallest bolt holds more than weight—it holds trust.
Why i3 Battery Mount Bolts Aren’t Just “Any Bolt”
The i3’s underbody battery is secured by 12–16 high-strength bolts (depending on model year), connecting the pack to the aluminum subframe. These aren’t decorative—they’re critical structural components.
Using incorrect hardware can lead to:
- Loose battery movement during cornering or impacts
- Galvanic corrosion between dissimilar metals
- Thread stripping in aluminum subframes
- Voided insurance claims in a collision (if non-OEM parts are found)
🔩 BMW specifies grade 10.9 steel with zinc-nickel coating—not stainless, not grade 8.8.
💰 Real Replacement Costs Compared
| Source | Price for Full Set (12–16 bolts + washers) | Risk Level |
|---|---|---|
| BMW Dealer | $280 – $420 (often bundled with labor) | Low (OEM) |
| Aftermarket Online (Generic) | $8 – $25 | High (wrong grade/coating) |
| OEM-Spec Supplier (e.g., FCP Euro, ECS) | $45 – $75 | Medium (verify specs!) |
| CNS BATTERY (Included) | $0 extra – full kit with every pack | None |
📌 Pro tip: Many “OEM-style” kits use stainless steel, which is softer and prone to galling in aluminum—BMW explicitly forbids it.
Exact Bolt Specifications for BMW i3 (All Years)
| Location | Qty | Part Number | Spec |
|---|---|---|---|
| Front Mounts | 4 | 07119906933 | M10x1.5×50, Grade 10.9, Zn-Ni coated |
| Rear Mounts | 8–12 | 07119906934 | M10x1.5×60, Grade 10.9, Zn-Ni coated |
| Washers | 12–16 | 07119906935 | Hardened, anti-rotation design |
⚠️ Critical: All bolts require torque + angle tightening:
50 Nm + 90° rotation (per BMW Repair Manual 61 12 020)
Skipping the angle step = insufficient clamping force = future loosening.
Why CNS Includes Correct Mounting Hardware—Every Time
When you order a CNS i3 battery pack, you get:
✅ Full set of OEM-spec M10 bolts and washers—pre-sorted and labeled
✅ Torque + angle instructions in the installation manual
✅ Anti-seize compound compatible with aluminum subframes
✅ No hidden fees—hardware is included in pack price
We’ve seen too many DIYers use Grade 8.8 hardware store bolts, only to return months later with rattling packs or stripped threads. That’s why we ship it right—so you install it right.
“I compared my old bolts to the CNS kit—same coating, same head marking, same length. Even the washers had the anti-rotation tabs. No guesswork.”
— Mark T., California
3 Common Bolt Mistakes That Cause Big Problems
- Using Stainless Steel
Softer than required grade—stretches under load, leading to loosening. - Skipping the Angle Torque
50 Nm alone isn’t enough. The 90° turn ensures proper preload. - Reusing Old Bolts
BMW classifies these as single-use stretch bolts. Reuse risks fatigue failure.
🛠️ Always replace—never reuse.
Frequently Asked Questions: i3 Battery Mount Bolts
Q: Can I buy just the bolts without a new battery?
A: Yes—but verify supplier specs match BMW 07119906933/34. Avoid “universal” kits.
Q: Do I need special tools?
A: A calibrated torque wrench and angle gauge (or torque-angle wrench). Not optional.
Q: What if I strip a thread in the subframe?
A: Requires helicoil insert by a qualified technician. Prevention is far cheaper.
Q: Are torque specs different for CNS packs?
A: No—identical to OEM. Our packs use the same mounting points and tolerances.
Q: Does CNS warranty cover bolt-related issues?
A: Only if original CNS hardware was used and installed per instructions.
Don’t Let a $12 Decision Undermine a $7,000 Investment
Your battery is the heart of your i3.
Its mounts are the hands that hold it safe.
Get the Right Hardware—Built In, Not Bolted On Later
When you choose CNS BATTERY, you’re not just buying cells—you’re getting a complete, engineered solution, down to the last bolt.
Skip the guesswork. Install with confidence:
👉 https://cnsbattery.com/ev-battery-home/ev-battery-contact/