| Detail | Value |
|---|---|
| Title | Battery Failure & Diagnosis — Sulfation, Shedding, Parasitic Draw |
| Target Length | 10-12 minutes |
| Format | Hands-on demo with 3D battery + DMM parasitic draw demonstration |
| Props | 3D battery, DMM (milliamp-capable), fuse box trainer or diagram, example batteries showing date codes |
SHOT: 3D battery on bench next to a DMM
NARRATION:
"A customer walks in and says 'my battery keeps dying.' That's a symptom, not a diagnosis. Is the battery bad? Is something draining it overnight? Is the charging system weak? In this module, we're going to cover why batteries fail — sulfation, plate shedding, cell imbalance — and how to diagnose parasitic draws that kill good batteries. Because replacing a battery without finding the root cause just means the next one dies too."
SHOT: 3D battery — point to Cell 5 (Sulfation label)
NARRATION:
"Let's start with the number one killer of batteries — sulfation. Look at Cell 5 on our 3D battery. The label here shows what sulfation looks like at the plate level."
SHOT: Remove an electrolyte cell, point to plate paste on grid
"During normal discharge, lead sulfate forms on the plates. That's fine — it's supposed to happen. When you recharge, the sulfate converts back to active material. But if the battery sits discharged — or never gets fully charged — that soft sulfate slowly hardens into crystals."
SHOT: Close-up of plate grid structure
"These hard crystals are like concrete. They don't convert back during normal charging. They block the plate surface, reducing the amount of active material that can participate in the chemical reaction. Less active material means less capacity."
SHOT: Whiteboard — list causes
"What causes it? Number one — chronic undercharging. The battery never reaches full charge, so some sulfate is always left behind. This is extremely common with short-trip driving. You drive ten minutes to work, ten minutes home. The alternator never runs long enough to fully recharge the battery."
"Number two — storage without a maintainer. A battery sitting on a shelf self-discharges. Over weeks and months, that slow discharge produces sulfate that hardens."
"Number three — low electrolyte level in flooded batteries. Any plate surface exposed above the electrolyte sulfates rapidly and permanently."
SHOT: Back to 3D battery
"Can you fix it? Sometimes. A slow charge at low amperage — two to five amps — over 24 to 72 hours can convert soft sulfation. But once it's crystallized, it's usually permanent. Prevention is the real answer — keep the battery charged."
SHOT: 3D battery — remove a plate grid from an electrolyte cell
NARRATION:
"The second failure mode is plate shedding. Look at this plate grid. The grid itself is a lead alloy framework — a lattice. The paste — lead dioxide on the positive side, sponge lead on the negative side — is pressed into this framework."
SHOT: Point to paste on grid
"Over time, this paste physically breaks away from the grid. Vibration from driving loosens it. Overcharging creates gas bubbles that push it off. Deep discharge cycles cause the paste to expand and contract, weakening the bond. Eventually, chunks of material fall off and settle at the bottom of the cell."
SHOT: Whiteboard — draw cell cross-section showing sediment at bottom
"That sediment builds up. Battery manufacturers design a space at the bottom of each cell — called the sediment well — to hold this material away from the plates. But eventually, if enough material accumulates, it bridges the gap between the positive and negative plates."
"When that happens, you get an internal short circuit. The cell voltage drops from 2.1 volts to near zero. One shorted cell takes your 12.6-volt battery down to about 10.5 volts. The battery is done."
SHOT: 3D battery — point to each of the six electrolyte cells in sequence
NARRATION:
"Count them — six cells, each producing 2.1 volts, wired in series to give us 12.6 volts total. In a perfect world, all six cells age at the same rate. In reality, they don't."
SHOT: Point to cells near one end of the battery
"The cells closest to the engine run hotter. Heat accelerates aging. So those cells wear out faster than the ones on the cool side of the battery."
SHOT: Whiteboard — draw six cells with voltages
"Let's say five cells read 2.12 volts and one reads 1.95 volts. Your total battery voltage is 12.55 volts. That looks almost normal. But under load, that weak cell can't deliver. It's like a chain — the weakest link determines the strength of the whole chain."
"If one cell shorts completely — say from sediment buildup — it drops to zero or near zero. Now you've got five cells at 2.1 volts. That's 10.5 volts total. The battery won't start the car."
SHOT: Close-up of 3D battery cells
"This is why a battery can read 12.4 volts and still fail a load test. The voltage looks acceptable, but one weak cell collapses under the heavy current demand of cranking."
SHOT: Bench setup — DMM, 3D battery, fuse panel image
NARRATION:
"Now let's talk about parasitic draw — also called key-off drain or dark current. Every modern vehicle draws some current from the battery even when the engine is off and the key is out. The clock needs power. The radio stores your presets. The body control module monitors the doors and the alarm system."
SHOT: Whiteboard — write acceptable ranges
"Normal parasitic draw is 25 to 50 milliamps. That's 0.025 to 0.050 amps. At 50 milliamps, a 60 amp-hour battery would take roughly 50 days to drain completely. In practice, the battery becomes unusable long before that — but the point is, 50 milliamps is sustainable."
"Above 85 milliamps, you have a problem. Something is staying awake that shouldn't be. At 300 or 500 milliamps, the battery could be dead in a few days."
SHOT: DMM on bench — set to DC amps
NARRATION:
"Here's how to test for parasitic draw. You need a digital multimeter that reads milliamps."
SHOT: Point to 3D battery negative terminal
"Step one — make sure everything in the vehicle is off. Lights, radio, HVAC — everything. Remove the key. Close all doors — but use a door latch tool to keep the door switch depressed so the interior lights don't trigger."
"Step two — wait. This is the step technicians skip, and it causes false readings. Modern vehicles have modules that stay awake for 20 to 60 minutes after you shut everything down. Some luxury vehicles take up to 90 minutes. If you test too early, you're measuring the module shutdown current, not the resting draw."
SHOT: Show DMM connection in series concept
"Step three — disconnect the negative cable. Connect your meter in series — one lead on the cable, one lead on the battery post. Set the meter to the highest amp scale first. On most meters that's 10 or 20 amps. This protects the milliamp fuse inside the meter. Once you see a low reading, switch to the milliamp scale for accuracy."
"Step four — read the value. If it's 25 to 50 milliamps, you're normal. If it's 85 milliamps or above, you've got a draw."
SHOT: Fuse panel image or trainer board
"Step five — if the draw is high, find the circuit causing it. This is the fuse-pulling method. With your meter still connected and showing the high reading, start pulling fuses one at a time. Pull one, check the meter. Did the reading drop? If not, reinstall that fuse and try the next one."
"When you pull a fuse and the reading drops to the acceptable range, you've found the circuit. Check the fuse label — it tells you which components are on that circuit. Then investigate each one."
SHOT: Whiteboard — list common draw sources
NARRATION:
"What are the usual suspects? Body control modules that won't go to sleep — often caused by a faulty door switch or hood switch. The module thinks a door is open, so it stays awake."
"Aftermarket accessories are a big one. A stereo system, alarm, dash camera, or LED light kit wired directly to battery power instead of switched power. When the car is off, they're still drawing current."
"Trunk lights and glove box lights. If the switch fails, the light stays on when the lid is closed. You can't see it, but it's draining the battery."
"Faulty relays — the contacts can weld together, keeping a circuit live permanently."
SHOT: Show a battery with date code sticker
"One more thing — battery age. Every battery has a date code. The most common format is a letter followed by a number. A through L for January through December, and a digit for the year. So C5 means March 2025. J4 means October 2024."
"Typical battery life is 3 to 6 years depending on climate. Hot climates shorten it — heat accelerates every failure mode we've talked about. If a customer has a 5-year-old battery with no draw and a working charging system, the battery is simply at end of life."
SHOT: 3D battery with Cell 5 and Cell 6 labels visible
NARRATION:
"Quick recap. Sulfation is the number one killer — caused by undercharging, prevented by keeping the battery charged. Plate shedding is a natural aging process accelerated by vibration, overcharging, and deep discharges. Cell imbalance means one weak cell can ruin an otherwise good battery."
"And when a battery keeps dying but tests good, look for a parasitic draw. Use your DMM in series, wait for modules to sleep, and use the fuse-pulling method to isolate the circuit."
"The Cell 5 and Cell 6 labels on the 3D battery summarize these failure modes. Review them before your next quiz."
"In Module 7, we'll cover battery safety — acid handling, explosion prevention, jump-starting procedures, and the PPE every technician should use."
| Shot | Description |
|---|---|
| B1 | Cell 5 Sulfation label close-up on 3D battery |
| B2 | Cell 6 Failure Modes label close-up on 3D battery |
| B3 | Electrolyte cells removed from 3D battery showing plate grids and paste |
| B4 | DMM set to milliamp range — display close-up |
| B5 | DMM leads connected in series at battery negative terminal |
| B6 | Fuse panel with fuses being pulled one at a time |
| B7 | Battery date code sticker close-up (real battery) |
| B8 | Whiteboard diagram of cell cross-section showing sediment buildup |
| B9 | Whiteboard drawing of six cells in series with one weak cell highlighted |