Car Hacking

12:22am | 04/19/2021
Daniel Tompkins

DIY culture electronics

03/12 Fish Fry Kerfuffle

If you're familiar with the Christian observation of Lent— meat is forbidden on Fridays. As a result, a lot of churches host Friday-night fish fry dinners, and I had been leaving to pick up my battered cod dinner.

Someone showed me an interactive fish fry map that'd been coded by Code for Pittsburgh. Side note: Code for Pittsburgh looks like a really cool gang of like-minded coders, and they've built some neat stuff together.

Screenshot from the official 2021 Pittsburgh Lenten Fish Fry Map from Code for Pittsburgh

Screenshot from the official 2021 Pittsburgh Lenten Fish Fry Map, created by Code for Pittsburgh.

Using the map, I picked out a church in nearby Shadyside. We pre-ordered two fried fish sandwiches for pickup at 5:45pm. Naturally, I was late, rushing to the car at 5:50pm, I rolled (it's low) into the front seat and slammed the doors. I could see the tartar sauce in my mind's eye ...

Then I turned the key ... nothing. Far too many of us have been in the same gut-wrenching situation. If you're less unlucky, you might still hear a click— or see the flash of a dash icon.

The stakes were still pretty low. I've been working remotely since September 2020. So, I'm blessed that I wasn't relying on the car to get to my job. In the grand scheme of things (WFH, pandemic, in the garage, on a Friday), this was probably the best-case scenario for a dead battery.

Jump-Starting a Dead Battery

My neighbor happened to be pulling into the driveway next door. So, in desperation, I hurriedly asked if I could get a jump. If you're like me and always forget the connection steps, enjoy this beautiful illustration by yours truly:

Diagram of hooking up a jump-start cable, showing 1. Pos Dead, 2. Pos Running, 3. Neg Running, 4. Ground Dead.

1. Dead battery's positive post to 2. The running battery's positive post. Next, connect 3. The negative post of the running car's battery to 4. The metal frame or other exposed ground on the dead car.

Apparently, you can also go from the running car's frame (#3), and connect (#4) to the dead battery's negative post. However, the above order is what I've most commonly seen (you're welcome future, stranded self).

We hooked up the cables. To my understanding, the alternator spins faster when you rev the engine— and, consequently, outputs a higher amperage. So, holding the pedal at about 2000 RPM might be productive— especially for bigger engines.

This should put out between 14V and 15V from an idling vehicle. If you measure less than 13V across the battery's posts while the car is running, then it's more likely you have an issue with your alternator (which charges the battery).

We must have let his car rev for at least 5 minutes without a click, blink or whisper from our Camry. In a last ditch, I tried biting into the battery's terminals using the jumper cable's copper alligator-teeth— still nothing. I thanked my neighbor for trying, but it seemed toasted— kaput.

Alas, it was not our destiny to taste the buttery, fishy flavor that night.

03/13 Camry Debugging

To recap:
Fish Friday. Yet no tangy-sweet tartar sauce.

My fiancée and I actually attempted (after some rapid deliberation) to bicycle across Pittsburgh's East End to the church.

Unfortunately, the hills of Pittsburgh are unforgiving to flat-land Illinoisers like myself. We also realized, after about a half-mile of biking, that the kitchen would definitely be closed by the time we would arrive.

I called the church, and they kindly said they'd comp the dinners we'd ordered for the next Friday. Without any pressing appointments or plans for the weekend, I made it priority one to get the car running— and to get those battered cods in one week's time.

Under the Hood

Saturday was an unseasonably beautiful day for March in Pittsburgh; so, I opened the garage door and ducked under the hood of the Camry. The first thing that stood out was the corrosion all over the battery's posts. It was heckin crusty and gross. 👇

That white (or bluish-green) powdery stuff is apparently either lead sulfate or anhydrous copper sulfate. As this corrosion builds up, so does the battery's resistance. No good.

I dug through the mantle of powder with the multimeter probes to find that the battery was reporting a mere 1.79V. That's close to 10% of the battery's full capacity.

Example of lead-acid battery post corrosion

That nasty business is lead sulfate or anhydrous copper sulfate. Hydrating anhydrous copper sulfate gives it the green or blue tinge. This NOCO blog post was a great resource for understanding battery maintenance and safety— plus I really liked the graphics.

Since the jump didn't work and the battery was reading an incredibly low voltage, my conclusion was that it needed to be replaced.

It's super easy to get the battery out. Doing this job on a Camry, a 10mm socket (I recommend a little box-end too for the terminal clamps) is probably the only tool you really need.

I recommend loosening the nut on each battery terminal clamp before the bolt tying this bracket to the frame. I made the mistake of taking off the bracket first and it was a pain to break the corroded nuts loose on the terminals with the battery loosy-goosy.

Once you get the front bolt out, there's a hooked tension-rod on the back that will need to drop down. Then you can pretty easily remove the bracket entirely. If you do it this way, you might be able to avoid dealing with the tensioning bolt at he other end of the bracket (see the image below).

Corroded battery still installed in Camry's engine bay. Red circle showing post-clamp tightening nut and the main bolt for the battery-retaining clamp bracket.
Corroded Toyota 2010 Camry battery sitting on the garage floor next to crescent wrenches and battery clamping bracket for mounting in car.

Really only 2 nuts and 1 bolt to get the battery out. Both the terminal clamp nuts and the bolt tying the battery bracket to the front of the car frame use a 10mm socket.

With the battery finally out, I looked around the outside to find a long string of letters and numbers that had been heat-stamped into the plastic:

The first letter refers to the month it was manufactured: A-L refers to January – December. The number refers to the year in which the battery was made. For example: 2 would be 2012, 3 would be 2013, 4 would be 2014, etc. The last letter refers to the plant in which the battery was made.1

My Toyota-manufactured battery had the number "8". Since the average lifespan of a normal car battery is between 2-5 years, it was most likely manufactured in 2018.2 R.I.P. battery, I promise to take better care of the next one.

Costco Membership

There are a couple stores (AutoZone, Advance Auto Parts, O' Reilly Auto Parts, Firestone, etc.) that will apparently test your battery for free. If you have a spare, it might be good to clean up the dead battery and take it over to them. You could find out if your battery is definitely shot or if the problem might lie elsewhere.

I was eager to get this fixed, so I went ahead and decided to purchase a new battery. Like any product, there are good and bad manufacturers. It can be helpful to read reviews and make sure you're getting your money's worth.

The only two things that are really important in purchasing a new battery are the battery "group" and the cold-cranking amps (CCA). The 2010 Camry uses group 24F, and the CCA needs to meet or exceed 582 (the CCA on the original, Toyota-manufactured battery). A quick cost-comparison among some of the nearby stores yielded these results:

Battery comparison. April, 4th 2021.


price + core



Advance Auto Parts

$169.99 + $22.00


3-year free replacement


$169.99 + $18.00


3-year warranty


$89.99 + $15.00


3-year limited warranty

Home Depot

$99.00 + $15.00


30-month free replacement

O' Reilly Auto Parts

$134.99 + $18.00


3-year free replacement


$98.76 + ?


3-year free replacement

The cheapest options by far were Costco, Walmart, and Home Depot. The "core" charge was a new concept to me (someone who has done little to no car repair); but it's important to note:

Certain types of auto parts can be recycled or, more specifically, remanufactured for future sale. These parts have a core price that is used as a form of deposit on the portion of the part that can be remanufactured and that is designed to encourage return of the old part. The "core," simply put, is your old part. Returning cores can save you money on replacement parts.3

TL;DR — make sure you recycle your old battery instead of tossing it out the window, because it could save you $20 on the new one.

Walmart didn't seem to advertise their core charge; regardless, I somehow convinced myself that the $60 Costco membership might be worth the $10 of savings for a Costco battery...

A generous friend gave me a ride to a nearby warehouse. This was my first time within 100 feet of a Costco, and that deserves its own story... but I'll stay on topic.

The sales rep recommended the ($120) "Gold Star Executive" membership and described the reasons why that was the way to go. There was visible disappointment when I revealed that I had knowledge of the $60 option.

After some very uncomfortable back-and-forth, I signed my soul away and got my picture printed on the plastic admission to the capitalist warehouse of wonders (in bulk).

We got back and plopped in the new battery. I hooked the tension rod back behind and tightened down the front of the bracket to the frame. There were a few articles online that recommended a mixture of baking soda and water for cleaning up the corrosion.

I soaked the terminal clamps, then brushed off the remaining corrosion with a stiff-wired brush. The same articles recommended using dielectric grease to prevent corrosion on the battery posts. I didn't have that readily available; but apparently petroleum jelly can be used as a substitute.4

The negative post gave a satisfying *pop* when I touched it back together— that's just an eager arc of electricity from completing the circuit to all the car's electronics. This time, when I turned the key, I could heard the familiar *chunk-chunk* of the starter before the engine revved to life. Success!

3/19 Charge Your New Battery

One week later, I was swimming in confidence and excitement. I had completed another successful home auto repair that had undoubtedly saved me hundreds of dollars in genuine Toyota parts, labor and B.S.

We were once again ready for delicious, holy fried fish. It was already paid for during the prior week's battery debacle. I rolled into the front seat, turned the key... and once again, the familiar fading dash lights of a dead battery.

Inconceivable (The Princess Bride)

This time, we had the time and fortitude to battle the hills of Pittsburgh. We biked to the church and got our fish sandwiches. It was worth the trip, but it was still a bittersweet meal knowing that our battery woes were to be continued...

The next day, I had my neighbor help me jump the car again. Thanks be to Zeus— god of electricity, it started. I swear, Nick, I won't ask you for another jump start for the rest of my life.

For real. As soon as we got it started, I drove to the nearest (actually, not the even the nearest) Walmart and bought a 120V plug-in charger.

We kept the car running for another hour or so, just to make sure the battery was getting topped-off.

Test for Parasitic Draw

Over the course of the next week, I took measurements across the battery posts. If the issue had been a parasitic drain— some short along the circuit that was pulling charge off the battery; then I might have had a real problem.

Measuring across the terminals while the car was running showed over 14V, confirming that the alternator was doing its job. After shut-off, the battery measured 12.79V (good). Over the course of a day, the battery dropped to about 12.5V. This seemed concerning at first, but then the voltage settled at about 12.47V and held.

12.79V measured on a Toyota Camry's battery after shut-off

Just a few minutes after shutting off the car, the battery measures 12.79V across the posts.

It was a pain in the butt; but I tested the electrical system for parasitic draw. I opened up the fuse compartments (there are actually two) on our 2010 Camry.

One is conveniently located under the hood (near the driver's side), and the other is unbelievably stupid-silly to get to— just behind the "kick-panel" trim (that plastic guard just under the steering wheel).

I wish someone had told me to really, truly exhaust every possible option before wasting your time hunting for parasitic draw.

To find the source of a parasitic drain on your battery, you essentially need to probe across every fuse until you find a circuit drawing power. From there, you'd get a ballpark of where to keep looking.

Camry fuse compartment under the hook

Seriously, imagine holding a multimeter probe to each of those tiny, exposed pads on each of those little fuses... no, thanks. Never again.

Additionally, to test for parasitic draw correctly, you should really have a charged battery. If you have a charged battery, then you can test voltage drop over time.

If the voltage drops quickly over the course of few hours (or drops below 12V) then you might have a reason to suspect parasitic draw. I definitely recommend watching this video by HumbleMechanic covering parasitic draw and how to test for it.

Car Repair Lessons Learned

About a month later now, and time to reflect. At the end of it all, I think it could have been that the new battery just hadn't reached a full charged.

It had sat for a week in a cold garage. You can't blame me— I'm WFH and we're still in a pandemic.

My best guess is that the small charge it received in the post-swap jaunt to the grocery store (one week prior) wasn't enough to keep it alive. I'm also convinced that one of the cheap USB dongles I bought at a gas station was jacked up (pun unintended).

Fingers crossed it was a glitch and the new battery will last at least another 3 years. At any rate, we now have an emergency charger for future Fish Fry Fridays.


1 How to Read US Battery Date Codes. US Battery. April 4th, 2021.

2 The Average Life of Car Batteries and 7 Tips to Extend Your Car Battery Life. Nationwide Blog. April 4th, 2021.,will%20last%20is%20the%20weather.

3 What is Core? NAPA. April 9th, 2021.

4 How to Clean Battery Terminals with Stuff You Already Have. Firestone Blog. April 4th, 2021.