New Battery and Alternator but Battery Still Drains: Common Causes and Solutions

It’s one of the most frustrating car problems – you just replaced your old battery and alternator but your vehicle’s battery is still draining too quickly. If this sounds familiar, don’t panic! There are several potential causes for a new battery draining, and identifying the issue is the first step to getting it resolved.

In this guide, we’ll go over the 8 most common reasons why a battery may continue draining even after replacement parts, as well as provide tips on how to diagnose and fix each problem. By the end, you’ll have the knowledge to troubleshoot what’s going on and get your battery lasting as it should. Let’s get started!

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New battery and alternator but battery still drains: Cause

Cause #1 – Short in the Wiring

A short circuit somewhere in the vehicle’s wiring harness can cause excessive battery drain by allowing electricity to flow to ground when it shouldn’t be. This puts extra load on the alternator to continuously recharge the battery and can quickly run it down.

To check for shorts, use a multimeter set to voltage mode and probe around connections while the vehicle is off. You’re looking for voltage readings higher than 0.5V, which indicates a short. Common culprits are wiring near moving engine components that may have rubbed through insulation over time. Repairing the short circuit will prevent further drain.

Cause #2 – Bad Ground Connection

If the negative battery cable isn’t making a solid connection to the vehicle’s chassis at the grounding point (usually the engine block), electricity won’t flow as it should when charging and extra resistance gets in the way. Over time this causes undercharge that leads to battery drain.

Inspect ground cable connections and clean contact points meticulously if corrosion is present. You can also add extra ground cables or replace if needed to ensure maximum conductivity. A parasitic draw test can help detect voltage drop across suspect ground points.

Cause #3 – Loose Battery Terminal

Corrosion builds up over time on battery terminals, eventually causing them to become loose and intermittent. This interrupts the charging circuit and prevents the battery from reaching a full state of charge. It then proceeds to drain down over repeated start/stop cycles.

So make sure to clean battery terminals with a wire brush or terminal cleaner and tighten securely. A clamp-on ammeter can detect draw going through terminals while wiggling them to find loose connections.

New battery and alternator but battery still drains

Cause #4 – A Problem in the Engine

A failing component like a leaky fuel injector or faulty ignition coil causes the engine to draw more cranking amps on start up and overloads the charging system, resulting in recurrent battery drain over a few days.

Start by inspecting for trouble codes with a scan tool. Pay attention to codes indicating injector leaks, coil failures, stumbles/misfires that point to a defective engine part increasing parasitic draw. Replacing the problem part removes extra load from the charging circuit.

Cause #5 – Blown Alternator Fuse

The fuse that protects the alternator circuit from overloads and shorts is an obvious thing to check if the alternator isn’t working properly. Pull it and inspect for discoloration or damage indicating a meltdown.

Be aware some newer vehicles have fusible links that can’t be replaced individually. Have a mechanic check the complete circuit from alternator to battery for any issues preventing proper voltage regulation and current flow. Replacing a blown fuse resumes alternator operation.

Cause #6 – A Problem in the Alternator Voltage Regulator

Even if the alternator spins and outwardly charges the battery at the correct rate, an internal problem with the voltage regulator can cause it to overcharge or undercharge intermittently. This stresses the battery through overcharging or prevents full charging respectively.

A multimeter set to DC voltage can monitor alternator output to check for fluctuations above 15V (overcharging) or below 13.8V (undercharging) that point to a defective regulator. Rebuild kits or replacement of the alternator is needed to resolve the root cause.

Cause #7 – The New Battery is Bad

As with any new product, it’s possible the replacement battery received was defective or damaged in shipping before even being installed. A bad cell inside won’t hold adequate charge like a healthy battery.

An easy test is observing the voltage level after a few hours without the alternator connected – it should remain above 12.4V and not drop below 12V for a “good” battery. If drain is rapid, the new battery itself may need warranty replacement. Always source from reputable suppliers.

Cause #8 – Damaged Serpentine Belt

An improperly tensioned or damaged serpentine belt won’t spin the alternator at optimal RPMs to produce sufficient charging power. This undercharges the battery each drive cycle and leads to drain over time.

Inspect the belt for signs of wear, tears/cracks. Have a mechanic check tension using a belt gauge tool – it should twang about midway between tight and loose when plucked. Replace belt if outside wear limits to restore alternator turning force.

How to fix car still die after replacing alternator and battery?

I know how frustrating it must be for your car to keep dying after replacing the battery and alternator. You’re probably feeling pretty puzzled right about now. But don’t lose hope – with some thorough troubleshooting, we can get to the root of this pesky problem.

First things first, let’s double check the basics. Give those battery and alternator connections a good scrub with a wire brush to remove any grime or corrosion. Then tighten them back up securely. You’d be surprised how many issues are caused by loose cables!

While you’ve got things apart, take a look at the serpentine belt too. If it’s cracked, glazing or stretched, it’s not spinning the alternator properly to charge up that battery. Replacements are inexpensive to solve that.

Next, pull out your multimeter tool and start tracing voltages. Check what’s coming off the alternator. Is it maintaining a steady 13-14 volts like it should? If not, the voltage regulator may need attention. This little component is crucial for battery juicing.

Don’t forget to inspect other charging system parts too, like the fuse box and relays. One worn out fuse could disrupt everything. These guys protect circuits from electrical overloads.

There’s also a chance something completely unrelated to charging is the real culprit. That’s where an expert mechanic ear comes in handy. They may pick up hints from diagnostic checks you can’t see.

Preventing Future Issues

While solving the immediate battery drain taking place now, it’s also wise to address any underlying issues that may cause repeat problems down the road:

Inspect battery terminals yearly for signs of corrosion and tighten as needed to maintain solid connections.
Check condition of wiring harness for rub-through damage and repair/seal as preventative maintenance every 2 years.
Replace old accessories like radios prone to developing electrical faults causing parasitic draws over time.
Keep alternator, belt and wiring connections in top working order with periodic proactive maintenance and replacement of worn parts.
Consider an onboard battery charger/tender if vehicle sits unused for long periods to keep it at full charge.

Taking these prevention steps will help your replacement battery and charging system stay in strong working order to avoid unnecessary premature failures and frustrations in the future. With the right diagnosis and fix, it should now last as long as it should!

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