SmartKey Fob Battery Dies— How To Enter Car, Start Engine, or Replace Battery

Overview

Did you know that when your SmartKey Fob battery dies, you still can enter your vehicle and start the engine? After I got a “key not found” message, I started the experiments shown in this video so that I can know whether I still can drive the car even if the battery is dead. I will explain how the auto keyless system works and I will also show you how to replace the battery if you choose to.

The example used in this video is a Nissan Leaf 2015. However many cars use the same system. It could be called SmartKeys, Keyless Entry, Keyless Go, Keyless Access, or Passive Entry system.

Alternative Methods

There is more than one way to approach this task. Here are the most common methods, ranked by difficulty and cost.

Auto Parts Store Replacement

Drive to an auto parts store where they will test your battery and often install a new one for free with purchase.

Difficulty: Beginner
Estimated Cost: $100-$250 for battery
Notes: Convenient — many stores offer free testing and installation

DIY Battery Replacement

Disconnect the negative terminal first, then positive, remove the hold-down bracket, swap in the new battery, and reconnect in reverse order.

Difficulty: Beginner-Intermediate
Estimated Cost: $80-$200 for battery
Notes: Save on labor; just make sure you have the correct group size

Roadside Assistance

Call AAA or your insurance roadside service for a jump start or on-site battery replacement.

Difficulty: Beginner-friendly
Estimated Cost: Free with membership or $50-$150
Notes: Best when stranded; some services sell and install batteries on the spot

Tips and Common Mistakes

Avoid these pitfalls and use these tips to get the job done right the first time.

Always disconnect the negative terminal first and reconnect it last to prevent short circuits.
Clean battery terminals with a wire brush and baking soda solution before installing a new battery.
Apply dielectric grease or petroleum jelly to the terminals after connecting to prevent corrosion.
Check that the replacement battery matches your vehicle’s group size, CCA rating, and terminal layout.
Some vehicles require an ECU reset or radio code after battery replacement — have these ready.
If the old battery has heavy corrosion, neutralize the acid with baking soda and water before handling.
Store batteries upright on a non-conductive surface — never place them on concrete in extreme cold.

Tools and Materials

Item	Estimated Cost
Replacement car battery	$80-$250
Battery terminal cleaner / wire brush	$5-$10
Wrench set (10mm, 13mm typical)	$10-$25
Baking soda (for corrosion cleaning)	$2
Dielectric grease	$5-$8
Battery terminal protector spray	$5-$8
Memory saver (optional, preserves settings)	$15-$30

When to Take It to a Mechanic

Not every repair is a DIY job. Take your vehicle to a qualified mechanic if:

You are unsure about the diagnosis — misdiagnosing the problem wastes money on unnecessary parts.
The repair involves safety systems (brakes, steering, suspension) — mistakes here can be dangerous.
Special tools or equipment are required that you do not own and would cost more than the shop labor.
The vehicle is under warranty — DIY repairs can void warranty coverage if something goes wrong.
You do not feel confident after watching tutorials and reading guides — there is no shame in hiring a professional.

Video Tutorial

For the full video tutorial, visit Genius Asian.

Continue learning with these related guides:

This article was originally published on cartrek.com on 2016-10-25. Content has been updated and expanded for 2026.