2014–2021 BMW i3
By Ray Delgado ✓ Certified Mechanic · Published Sep 21, 2026 · Updated Oct 22, 2026
Save $168 by doing it yourself! Shop cost: $315
Quick answer: Battery Replacement on a 2014–2021 BMW i3 is rated Moderate and takes about 45–60 minutes. You'll need 6 tools for this job, and parts cost about $147. This guide walks you through the full job step by step, including the mistakes to avoid.
| Part Name | Part Number | Price | Buy |
|---|---|---|---|
| Correct group-size battery | — | $140.00 | |
| Terminal cleaner Optional | — | $8.00 | |
| Terminal protectant | — | $7.00 |
About prices: shown prices are typical retail averages and change frequently; cheaper alternatives may be available. Confirm the current price before buying.
💡 Pro tip: Order all parts at once to save on shipping
Follow these steps carefully
Put on safety glasses and gloves. Gather your Torx bits, 10mm and 13mm sockets, and your OBD2 adapter with a battery-registration app, because the i3 will want the new battery registered afterward.
Remove the Torx screws holding the frunk trim covers and lift the covers out. Then lift out the frunk storage bin itself — the 12-volt battery sits underneath it on its tray.
Before touching the 12-volt terminals, pull the high-voltage safety connector — the green plug in the frunk area — straight out to isolate the high-voltage battery, as shown in many i3 DIY videos. Then, with a 10mm socket, loosen the negative (black, minus) terminal first and lift the cable end off the post. Tuck it aside so it cannot spring back. Repeat with the positive (red, plus) terminal. Keep your tools clear of the orange high-voltage connectors for the entire job.
I make it a point to pull that green safety connector before touching anything else — it isolates the high-voltage battery. Orange cables and green plugs: hands off, tools off. The 12-volt job is easy; the high-voltage system is not where you learn by trial.
Unbolt the metal bracket that clamps the battery down — usually a 13mm bolt — and set the bracket aside. Pull the vent tube elbow off the side of the battery so the battery can come out freely. The windshield washer filler tube crosses over the area on many i3s; unclip it or lift it gently aside rather than forcing the battery past it. Note exactly how the vent and filler are routed, because they go back the same way. Take a quick photo of the battery orientation before you move it.
Lift the old 12-volt battery up and out of the frunk tray. The i3’s battery is a compact AGM unit, and BMW fits special brass terminal adapters onto its posts — unbolt these adapters from the old battery and transfer them onto the new one, because the car’s cable ends are sized for them. Check the new battery against the old for identical size, polarity, and terminal positions. If the tray has leaves or grime in it, wipe it out now while access is easy.
In my experience, those little brass terminal adapters are BMW-specific — lose them and the cables won't fit the new battery. Unbolt them off the old one and transfer them over before you do anything else.
Lower the new battery into the tray in the same orientation as the old one, with the brass adapters already fitted to its posts. Refit the metal hold-down bracket and snug its bolt so the battery cannot move. Push the vent tube elbow back onto the battery’s vent port and re-route the washer filler tube exactly as it was. Now reconnect the cables in reverse order: positive (red) first, then negative (black) last, tightening each 10mm nut until the cable end is snug and cannot twist on the post. A light coat of terminal protectant keeps corrosion away.
Push the green high-voltage safety connector back in until it seats, then refit the frunk storage bin, the trim covers, and their Torx screws. Your clock will need resetting, and take a short test drive to confirm everything behaves. Power the car on and confirm there are no drivetrain or 12-volt warnings.
Test your repair before closing everything up. If something doesn't work right, double-check your steps.
⚠️ Common Mistakes to Avoid
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