# Bringing a Car Battery Back from the Dead: A Ch00ftech Halloween Tale

Yesterday, I hopped into my car to take a drive to Goodwill for some Halloween costume parts when I noticed that my car’s battery was dead.  Very, very dead.

# Background

I really don’t drive that often.  In fact, I didn’t really realize how little I drive my car until I tried to start it yesterday.  Turns out, I haven’t sat in the driver seat since before I left for China.  A week before in fact.  I’m coming up on two months now of non-driving.  On top of that, I had apparently left the cabin light on the entire time, so it’s not much of a surprise that the battery didn’t make it.

The smart thing to do in this kind of situation is to get someone to help you jump-start your car, but there are rarely other people in my parking garage, and that’s too boring anyway.  I ended up removing the battery from the car and charging it on my own.

Unfortunately, I wasn’t really anticipating this project turning into a blog post, so I don’t have too many pictures or other documentation.  This is a very text-heavy post.

# Disclaimer

Car batteries can put out a metric crap load of current.  We’re talking like 60-70 Amperes easily.  This amount of energy can be extremely dangerous if not handled correctly.  I hope that you learn a thing or two from this post, but I do not advocate that anyone attempt what I tried in this post.  If it makes you feel any better, following this guide will only fix your battery enough to drive you to Pep Boys so you can recycle your permanently damaged car battery and replace it with a new one.  It’s probably not worth your time to follow my steps.

So, right.  When I went out to start my car, it was dead.  I mean DEAD.  I might as well have had the battery disconnected.  Grabbing my voltmeter, I measured 0.16V across the terminals.  This is a pretty bad sign.  Regardless of the chemistry, once most batteries are fully discharged, they are permanently damaged.

I promptly removed the battery and brought it up to my apartment.

WIthout doing too much research before hand, I knew that I would need to dump quite a bit of current into the battery to bring it back to life.  I knew from my work with Li-ion cells (and just about any sort of electric energy storage technology), that this battery was going to suck up a lot of current at the beginning and then take progressively less until it was fully charged.

You can model most batteries as a voltage source in series with an internal resistance.  Car batteries have very low internal resistances, and dumping 12V across this was bound to reach very high currents.

# Conclusion

So yes, that was quite a bit of work to put into a battery that I ended up recycling, but I did save myself the $40 it would have cost for a battery charger that I would have used a single time. I also learned quite a bit about lead acid battery chemistry and charging profiles, and I hope you did too. Happy Halloween! ## 42 thoughts on “Bringing a Car Battery Back from the Dead: A Ch00ftech Halloween Tale” 1. The other way batteries like this fail is the compound (lead sulfate) on the plates flakes off and settles in chambers at the bottom of the battery. When these chambers are full the compound shorts out the plates and that it’s over. One feature of the deep cycle batteries is deeper chambers to hold more crap. There are other differencing with the deep cycle batteries but this is a big one. The main issue with the lose of compound is reduced capacity which normally is OK. Check out the Wikipedia page on lead acid batteries, it has quite a lot of useful details. http://en.wikipedia.org/wiki/Leadâacid_battery • There’s a new way called EZbattery (www.EZbattery.info) to bring nearly any type of old battery back to life so it’s just like new again. This method works with nearly every type of battery out there …and it’s simple and quick. In case you’re wondering, you’ll be able to bring car, phone, and laptop batteries back to life with this. It even works with solar/off-grid, marine, golf cart, and forklift batteries. Plus, many more! • There’s nothing new in the EZbattery method except more ‘replies’ like this which are ads written by the EZbattery folks. 2. A very creative solution, I’ve also found that PC powersupplies are very good high current sources. 3. Considering you don’t use your car that often, a battery maintainer should keep yours safe from a full discharge. Sure, they cost about as much as a charger, but can be plugged to the 12V in-dash socket and will float or charge automatically as needed. I have one myself and it does a pretty good job. http://www.amazon.com/Black-Decker-BM2B-Automatic-Maintainer/dp/B000AMOEPA 4. Very nice write-up and great methodology! So, with a bit of care and attention, I could theoretically charge my 115ah sla with an atx supply? • Why didn’t you just use a 12v dc charger from any electrical charger like a router for instance . It pushes a couple amps and 12v ? 5. I thought that if you monitered the voltage regularly with a Digital Volt meter and it is lower than 12.6 or 12.7 volts you should be thinking about a new battery. On the other hand if you measure a satisfactory Voltage,the next morning the Battery could short out and be dead. • Keep reading! You’re absolutely right. The method I used was only meant to give me enough juice to make it to the store to buy a new battery. It is by no means a permanent solution. It’s also dangerous as hell, so don’t do it. 6. It’s amusing to me really. You certainly did some serious over thinking there. Here’s how to get a charge: Asprin. Yes, one crushed asprin in the water would give sufficient charge to start and then let idle for half an hour. Failing that, drain the battery, add hot water and a pinch of epsom salt into each cell. Chemistry trumps Electrical Engineering, I’m afraid. • Huh…I’ve never heard of that. I might have to start keeping some aspirin in my car… 7. you should have used -5V and +12V from the PC power supply. 17V would have done it without any diodes, capacitors,etc. Also ATX power sources are protected on short-circuit, in which case (higher amperage than nominal) a simple resistor would do the trick…., or with some more creativity a capacitor serialized on 220VAC ATX input. 😉 But hey, thumbs up for the effort 🙂 • The negative rails on ATX supplies are mostly depreciated and most can supply less than an amp of current which would have been less than what I was doing with my solution. It could work, but more than likely, the power supply would just shutoff. I could do it with a current limiting resistor, but I’d either need something fairly high power, or just be willing to wait a lot longer to get it to work. I don’t normally stock high power resistors, but I could have made one out of a piece of pencil lead. Good suggestions though. I didn’t even think about the negative rail. 8. I was faced with a battery having only 1.8 volts after my car was not used for 5 weeks. A search on the web brought me here but I am from the KISS school. The battery charger just did not want to know so, I borrowed someones car battery and with jump leads connected both batteries together. After a few minutes the voltage on the dead battery was up to around 6 volts and I was able to use the battery charger for the rest. 9. I just put aspirin into my battery along with Epsom salt and now the front right end of my car is missing. The fricken battery just melted and slowly took the metals and other plastics with it and I’m so scared right now I think I’ll be making payments on a car that I don’t think can be fixed cuz half the frame in melted 😐 • IS IT SERIOUS? SORRY BUT I CAN’T STOP LAUGHING COS YOUR STORY IS VERY FUNNY………hihihi 10. Even if you had not left the dome light on, most cars have enough phantom loss (clock, computer, alarm, etc) to go dead in 2-4 weeks. Since I park mine longer than that, I found the solution is a battery disconnect (any auto parts store should have them, about$10). When I park the vehicle, lock all the doors (can’t do it once power is off) and remove the hand twist bolt and store it securely (do NOT lose it) and then close the hood and doors. I have come back many weeks later and battery is still able to start car. Batteries don’t self-discharge very fast.

PS You are very lucky not to be blind or burned with sulfuric acid.

11. I must admit to having a lot of tools at my disposal because I am a farmer but the trouble you went through is mind boggling. I have had the same problem with cars, trucks and farm equipment many times and usually get at least another year or two after a full recharge. I know that living in the city you don’t have space for lots of extra things so I partly understand why you went to such extreme lengths.

I have a few pieces of equipment that sit around for long periods of time and I do have a trickle or maintainer charger connected to them. The cost in very low., maybe thirty to forty dollars each. On the ones that do run down I either connect a regular charger to them or if I need it quick I just jump it. After a few hours of running the batteries usually hold charge again.

12. A battery maintainer does seem like a pretty good idea for you, so that you don’t end up killing another $100 battery. Harbor freight has them for a *lot* less than$40 – currently they’re on sale for $6.99, and regular price is only$15. Curiously, they have three different model numbers (#42292, #69594, and #69955) which all seem identical – including the prices.

These things are the epitome of simplicity. They’re comprised of a wall wart (probably 16 volts or so), a little electronics module, and a couple of battery clips on a coily cord. Opening up the electronics module reveals a LM317 regulator wired so that it provides constant current (1 amp, supposedly) until the battery voltage rises to a preset value (probably around 14 volts). At that point it switches to a constant voltage source to maintain the battery at full charge.

This simple circuit actually works great (it’s called a two-mode charger; three-mode chargers exist which deliberately overcharge the battery for a little while to “equalize” the cells, making sure they’re all fully topped off). And for the price, it can’t be beat. (I actually stole the clever little circuit to use in an embedded product I built – worked great there, too.)

Great blog – I look forward to the next episode!

13. Pingback: Car Battery Dead | autoksk

14. Awesome!

An electrical engineer who believes that a car battery is 12 volts! I stopped reading there. As my physics teacher said repeatedly, ” a little bit of knowledge is dangerous”.

• Because that 0.6V really makes all the difference!

Thanks for the tip though. I always assumed they were 12. Either way, if that scares you, don’t read the rest of the article. I broke a …lot of rules.

• Actually, a brand new car battery, fully charged, will read slightly more than 13 volts. As they age, their fully-charged voltage will become less and less. A car battery that only has a maximum charge of 12.6 volts is clearly several years old.

Never, ever assume – especially when working with cars. You can get yourself into hot water, even being an electrical engineer. There are vehicles with “positive earth”. Stay safe!

15. If you bought the $40 battery charger, couldn’t you just keep it as a high current power supply for some other project? There is a Harbor Freight version that can supposedly supply 55 amps in car start mode. Oh, and I have a couple of the really cheap Harbor Freight battery maintainers. They work fine. I ruined one because I wasn’t aware of how delicate the wire is on the 120 volt side. • They can supply a lot of current, but only in the context of charging. A battery charger will start reducing current as soon as you reach optimal voltage. For$40, you can do better with some PC power supplies or even put it towards some nice purpose-built lab equipment.

16. Well, this didn’t help me save my battery one bit, but certainly interesting to read. Glad you had fun!

17. Awesome article. i learn a lot from it to revive my batteries. Thanks

18. hilarious

19. Thanks for your creative way! Now I can recycle my permanently damaged car battery and replace it with a new one.

20. Wow, you’ve done such a great solution. I’ve pin this post for using in one day that my car battery is dead. Thank you for sharing this.

21. Great post! Thanks so much for sharing such a experience!

22. All I do is get my car to a garage and have it repaired by a mechanic, but your post is still interesting to read, thanks for share!

23. One of the easiest ways to save my money when the battery is dying. Thanks for awesome post.

24. Great, you’re like an automotive expert. Batteries need to be maintained, recharged after long periods of unused. Thank you for sharing this tutorial.

25. Maintenance car battery is an important thing to do occasionlly

26. Good article except I have seen V8 engine starters briefly draw over 1000 amps, a little more than you mentioned. You are a bold man to try what you did, be careful.