Fixing Your 2020 4Runner's No-Start and Electrical Weirdness

How to Fix Battery Replacement

When your 2020 Toyota 4Runner won't start or exhibits strange electrical behavior, a failing battery is often the root cause. This guide compiles real-world experiences from owners to help you diagnose, replace, and prevent battery issues. As one owner, Electronic_Low_9598, shared about a frustrating no-start situation: “It figured its self out and eventually started. I couldn’t come up with a fix, tried checking battery and restarting the keyfob but it only started when it was ready.” This sentiment of intermittent, confusing symptoms is common, and a systematic approach is your best defense.

Symptoms

Owners report a range of confusing and intermittent symptoms that point toward a weak or failing battery. The most common is a no-start condition, where the truck simply won't crank. This isn't always consistent; the vehicle may start normally one moment and then refuse the next, leading to a feeling of random "weirdness" in the truck's behavior. This unpredictability is a hallmark of a battery on its last legs.

Another symptom tied to low power is strange behavior from the security and immobilizer system. When battery voltage drops, the computer modules that manage your truck's security can malfunction. This can prevent the engine from starting even if you hear a click or the dash lights up. As owner TJS1138 noted, “Apparently, it's a security system issue, but I can't troubleshoot a cause.” This link between a weak battery and phantom security glitches is a critical clue.

You might also experience issues with the key fob. A low battery in the truck can sometimes interfere with the fob's signal, or the symptoms can mimic a dying fob battery itself. One owner, CrayonMayon, described a workaround: “This is what’s happened to me when my fob battery is low. Tagging the start button with the fob seems to jolt it to life.” While this trick can help with a bad fob battery, if you're also having general electrical issues, the primary 12-volt battery under the hood is the prime suspect. Other signs include flickering interior lights, slow power window operation, or the infotainment screen resetting itself.

Most Likely Cause

The primary cause of these starting and electrical issues, based on owner reports and diagnostic patterns, is a degraded 12-volt starting battery suffering from internal shorts or a significant loss of capacity. Car batteries have a finite lifespan, typically 3-5 years. Over time, the internal plates sulfate, the electrolyte degrades, and internal resistance increases. This leads to an inability to hold a sufficient charge, especially under the high-demand load of starting the engine.

An internal short within the battery cells is a specific failure mode that owners have mentioned. This creates a parasitic drain inside the battery itself, causing it to go dead overnight or after sitting for a short period. It also leads to inconsistent voltage output, which explains the random "weirdness" and electronic glitches. The truck's sensitive computers require stable, clean voltage to operate correctly. When a dying battery provides weak or fluctuating power, modules for the immobilizer, drivetrain, and infotainment can behave erratically, throwing warning lights or refusing to allow a start. The "fuel system" cause mentioned in the data often manifests as a no-start because the fuel pump and injectors won't receive the proper power to prime and operate if the battery voltage is too low.

How to Diagnose

Before rushing to buy a new battery, a proper diagnosis will save you time and money. You'll need a digital multimeter, and ideally, a dedicated battery load tester for the most accurate results.

Start with a visual inspection. Open the hood and check the battery for obvious signs of failure: bulging or cracked case, significant corrosion on the terminals (white or blue crusty deposits), or leaking electrolyte. Next, perform a voltage test. Set your multimeter to DC volts (20V range). With the truck completely off, connect the red lead to the battery's positive (+) terminal and the black lead to the negative (-) terminal. A healthy, fully charged battery should read between 12.4 and 12.7 volts. Anything below 12.2 volts indicates a low state of charge and may be the cause of your problems.

The most telling test is checking voltage under load. Have a helper turn the ignition to "START" (or crank the engine if it will) while you watch the multimeter. A good battery should maintain a voltage above 9.6 volts during cranking. If the voltage immediately plunges below 9 volts, the battery lacks the necessary cranking amps and is failing. If you have a dedicated load tester, follow its instructions. It applies a calibrated load and gives a pass/fail reading on the battery's health. As owner RoughIndependence340 demonstrated, monitoring health is key: “Tested it yesterday and it still at 93% health on my battery tester.” Finally, rule out a parasitic drain from an aftermarket accessory. If you've installed dash cams, lights, or chargers with incorrect wiring, they can drain the battery. As DeathByPetrichor warned about adding USB ports: “Just make sure you tap into one that’s only on with the ignition or you will drain your battery.”

Step-by-Step Fix

Replacing the battery in your truck is a straightforward DIY job. Follow these steps to do it safely and correctly.

Step 1: Safety First. Park on a level surface, set the parking brake, and turn the ignition OFF. Put on safety glasses and gloves. Battery acid is corrosive.

Step 2: Locate and Identify. The battery is located in the engine bay on the driver's side. Note the orientation of the positive (+) and negative (-) terminals. The positive terminal will have a red plastic cover and is connected to multiple red wires.

Step 3: Disconnect the Negative Terminal. This is the most important safety step. Using a 10mm socket and ratchet—as owner TJS1138 succinctly put it, “a 10mm socket, and a ratchet are going to be your friend”—loosen the nut on the negative terminal clamp. Carefully lift the clamp off the terminal and secure the cable away from the battery so it cannot accidentally make contact.

Step 4: Disconnect the Positive Terminal. Now, remove the red plastic cover (if present) and use the 10mm socket to loosen and remove the positive terminal clamp. Tuck this cable safely aside as well.

Step 5: Remove the Hold-Down Bracket. The battery is secured by a hold-down bracket that runs across the top or side. This bracket is typically secured by a 10mm or 12mm bolt. Remove this bolt and set the bracket aside.

Step 6: Remove the Old Battery. Batteries are heavy (30-50 lbs). Carefully lift the old battery straight up and out of its tray. Place it on the ground away from your work area.

Step 7: Clean the Tray and Terminals. Inspect the battery tray for corrosion or debris. Clean it with a baking soda and water solution (neutralizes acid) and a wire brush if needed. Also, clean the inside of the terminal clamps on the vehicle's cables until they are shiny metal.

Step 8: Install the New Battery. Lower the new battery into the tray, ensuring it is oriented the same way as the old one (positive terminal on the correct side). Reinstall the hold-down bracket and tighten the bolt securely, but do not overtighten and crack the battery case.

Step 9: Reconnect the Terminals. This is critical: Connect in REVERSE order. First, connect and tighten the positive terminal clamp. Then, connect and tighten the negative terminal clamp. Ensure both connections are tight and secure.

Step 10: Reset and Test. After reconnection, you may need to reset your clock, radio presets, and power window auto-up/down function (roll each window all the way down and then all the way up, holding the switch for a second at each extreme). Start the engine. It should crank vigorously and start immediately. Let it run for a few minutes to allow the alternator to begin charging the new battery.

Parts and Tools Needed

Parts:

• Group 24F or Group 35 Battery: These are the common sizes for the 5th-gen 4Runner. Always double-check your owner's manual or the label on your old battery. Popular OEM-style replacements include the Toyota-branded battery or aftermarket brands like Interstate, DieHard, or Optima.
• Terminal Protector Spray (Optional): A small can of anti-corrosion spray to coat the terminals after installation and prevent future buildup.

Tools:

• 10mm Socket and Ratchet (Essential, as per owner advice)
• Socket Extension (3-6 inch, helpful for the hold-down bolt)
• Wire Brush or Battery Terminal Cleaner
• Safety Glasses
• Gloves
• Digital Multimeter (for verification)

Real Owner Costs

The cost to replace a battery ranges significantly based on whether you DIY or use a shop, and the brand of battery you choose.

DIY Cost Example:

• Economy Battery: As owner RoughIndependence340 found, “This is the best bang for your buck 69 bucks, mines running strong after three years.” A basic, reliable battery can be found for $70-$120.
• Premium Battery: AGM (Absorbent Glass Mat) or high-performance batteries range from $180 to $300.
• Tools: If you don't own them, a basic socket set is $20-$40.
• Total DIY Range: $70 - $340, with most owners spending around $150 for a quality mid-tier battery.

Professional Service Cost:

• Parts Markup: Shops typically mark up the battery cost by 30-50%.
• Labor: Most shops charge 0.5 to 1.0 hours of labor for testing, replacement, and system reset. At an average rate of $120/hr, that's $60-$120.
• Core Charge & Disposal: A core charge (refundable when you return the old battery) of $15-$20 is standard, plus a small disposal fee.
• Total Shop Range: $200 - $500+, with an average cost likely between $250 and $350 for parts and labor.

The DIY savings are substantial, often cutting the cost in half or more. The job requires minimal mechanical skill, making it one of the most cost-effective repairs you can do yourself.

Prevention

Preventing premature battery failure involves a mix of maintenance and smart usage habits. First, keep the terminals clean. Periodically inspect for corrosion and clean it with a wire brush and baking soda solution. Dirty terminals create resistance, making it harder for the battery to charge and discharge properly.

Minimize parasitic drain. If you install any aftermarket electronics (dash cams, lighting, chargers), ensure they are wired correctly to a fuse that is only powered when the ignition is on. An accessory wired to constant power will slowly drain the battery, especially if the truck sits for days. Avoid short-trip driving. Frequently driving for less than 15 minutes doesn't give the alternator enough time to fully recharge the battery used during startup. If your truck sits unused for weeks at a time, consider using a battery maintainer or trickle charger. These devices plug into a wall outlet and keep the battery at an optimal charge level without overcharging it. Finally, have the battery tested annually, especially as it approaches the 3-year mark, to catch a decline in health before it leaves you stranded.

What Owners Say

Real experiences from TOYOTA owners:

Owner Experiences

"This is what’s happened to me when my fob battery is low. Tagging the start button with the fob seems to jolt it to life." — CrayonMayon (source)

"Apparently, it's a security system issue, but I can't troubleshoot a cause. But a 10mm socket, and a ratchet are going to be your friend in the future." — TJS1138 (source)

"Mine has this issue every now and then, but it might be since I put in the immobilizer. Disconnect the battery, and re-connect." — TJS1138 (source)

Pro Tips from Owners

💡 "Personally I would just add a fuse tap into one of the fuses in the fuse box by your feet. Just make sure you add the proper fuse and make sure you tap into one that’s only on with the ignition or you will drain your battery." — DeathByPetrichor (source)

Real Repair Costs

"This is the best bang for your buck 69 bucks, mines running strong after three years. Tested it yesterday and it still at 93% health on my battery tester." — RoughIndependence340 (source)

FAQ

Q: How long does it take to replace the battery? A: For a first-timer with all tools ready, the physical replacement takes 20-30 minutes. Allowing time for cleaning the tray and terminals, and resetting electronic features, budget about 45 minutes to an hour total. It's a very quick job for an experienced person.

Q: Can I drive with a failing battery? A: It is not recommended. A battery that is failing under load can leave you completely stranded without warning. Furthermore, a weak battery forces the alternator to work harder to try to charge it, which can lead to premature alternator failure—a much more expensive repair. Address a suspect battery immediately.

Q: Is this a common issue on the 2020 4Runner? A: While not a model-specific defect, battery failure is a universal wear-and-tear item common to all vehicles. The 2020 model is now entering the typical 4-5 year lifespan window where original equipment batteries begin to fail, so owners are increasingly reporting these issues. The security system glitches related to low voltage are a frequently noted symptom specific to modern, computer-heavy vehicles like this truck.

Q: DIY vs mechanic - what's recommended? A: This is a highly recommended DIY job. The steps are simple, the risk is low if you disconnect the negative terminal first, and the cost savings are significant. The only special tool you absolutely need is a 10mm socket and ratchet. If you are completely uncomfortable working under the hood or have physical limitations, a professional installation is perfectly fine, but you will pay a premium for the convenience.

Q: Why do I need to reset my windows and radio after a battery change? A: When you disconnect the battery, you remove power from the vehicle's body control modules. These modules have a learned memory for certain functions, like the one-touch up/down feature of the power windows. The radio may lose its security code (if equipped) and presets. The reset procedures are simple and outlined in your owner's manual; they allow the computers to relearn their reference points.

Q: My truck won't start even after a new battery. What now? A: As one owner discovered, a security/immobilizer glitch can persist. TJS1138's fix was: “Mine has this issue every now and then... Disconnect the battery, and re-connect.” Try disconnecting the negative terminal for 15-30 minutes to perform a "hard reset" on all the truck's computers. Reconnect and try again. If the problem remains, the issue could be a faulty starter, bad connection at the battery cables, or a failing ignition switch, and further diagnosis is needed.