2 Volts on Car Battery

Question

My car battery has gone completely flat after leaving my car parked up for about a month. Tried turning over the car today, and none of the lights on the dash light up.

Ran a multimeter across the terminals, and it shows 2 volts. This battery is under a year old in age, and has never been jumped before. It is a value brand battery, so cheap and not great. I can jump the car, but I imagine it will put undue stress on the alternator.

Is it even worth my time bringing the battery to the local car parts place for a trickle charge, or should I bite the bullet and get a new battery for roughly 100EUR ?

Answer 1

Lead sulfate crystals form on the battery plates as the battery discharges. As the battery becomes more discharged the crystals go from being soft and fluffy to much harder. Recharged in time, the lead sulfate is converted back into sulfuric acid and lead. A month is entirely too long for a battery to remain discharged.

Reversing a serious sulfation condition, even for high quality deep cycle batteries, requires special battery chargers which are able to charge at higher voltages (about 15 volts) than what most consumer-grade chargers produce (about 14.4 volts) and well above what trickle chargers produce (about 13.8 volts).

Car batteries aren't deep cycle batteries, they are "Starter, Lights, Ignition" (SLI) batteries with thinner and more numerous plates, designed to provide very high current for very short periods of time. Attempting to perform the controlled over-charging needed to equalize an SLI battery can cause the plates to warp from the heat, or shed plate material and develop shorts.

The long and short of it is that your battery is pretty much ruined. You might be able to get it to appear to hold a charge, but sulfated batteries have significantly reduced capacity due to reduced active plate surface and material.

This is to go-to web site for most battery questions.

http://batteryuniversity.com/learn/article/equalizing_charge

Answer 2

Since you have a battery which isn't that old (most batteries have about a five year life span), I'd suggest you put it on a charger and try to recharge it. This will allow the battery to come back to full charge without putting an undue stress on your alternator. You have to decide if the time spent in recharging the battery is worth your time. To me, 100EUR would be well worth my time as long as I have a spare vehicle to utilize in the mean time.

While this episode of having to recharge the battery will have taken a toll on the battery (shortened its lifespan), it will most likely be able to take the charge and will work fine for you for the foreseeable future.

Another thing to think about, though, is if the battery is only a year old, it may still have the manufacturer's warranty in place. If this is available, you may just take it in and say, "I'll take my replacement, please." ... especially if there is a priority need for the vehicle.

Answer 3

I don't think you are likely to "put undue stress on the alternator." It is a myth in my opinion that alternators can't handle charging a battery, Alternators are literally motors run in reverse and are designed to handle a lot of current. The only issue with charging a batter is it will get a bit warmer than usual and that shouldn't effect it as long as it dosn't get so hot you melt the insulation.

Answer 4

If the battery puts out just 2V across the terminals then it is severely discharged; in all probability beyond the point of recharging.

There's no point in trying to charge it. I've had a battery that put out only 9V which couldn't be revived.

Answer 5

A 12v lead acid battery is flat dead at no less than 10v. If it really were 2v, that would indicate that several cells had shorted out, and you wouldn't even be able to jump start it, as the battery itself would be burning off most of the power the jumper cables can transfer as heat. The fact that you managed to jump it indicates that you read it incorrectly. Double check your multimeter settings ( make sure it reads 12-15v on the running car you are using as the power source to jump ). If you somehow did measure it right, and still managed to jump it, it is a miracle and you should drive straight to the auto parts store and get a new battery.

Answer 6

From personal experience 2V is way under the safe discharge zone (considering yours is the typical lead-acid). Your battery is now damaged. Even if you charge it with an industrial charger and miraculously get it back to 13.2 Volts (of full charge) you will still get a lousy capacity and current discharge. In the best case scenario you will get a few seconds to start the car but not enough charge for a second or third try (in case it won't start the first time).

In your case i would attempt a revival if it was below 20$ (if you urgently need it and don't want to hasty buy the first battery you find). You could also buy a charger and try to revive it yourself (basic ones go for 20-30$ on amazon). But even if i revived it i would still pay the 100$ for a new one as soon as possible (I wouldn't want to pray every time i start) and maybe keep the old one in my trunk just in case i need a little extra charge.

Please remember to disconnect the battery if you intend to leave your car idle for more than two weeks.

Answer 7

I think only you can decide if it is worth your time and money to take it out and get it charged compared to purchasing a new battery.

To assist, if we assume a car battery will last 5 years, and you have had it for, say, 1 year, then you would expect this battery to provide another 4 years of service which I'll say is a value of 80EUR.

But if, as others believe, that this battery has lost life then you may not get another 4 years of service - without any justification, say you only get 2 years of future service, compare your time and costs against a battery with a value of 40EUR.

Re 2V: it would be odd that with load removed that you are getting 2V. This suggests that 3 of battery cells have gone reverse polarity or that 5 cells are shorted or some combination (I will not consider shorted cells beyond this point since, without justification, I will deem to be terminal).

Given that this took place over 1 month, then there are 2 possibilities:

1) your car has some fault that is discharging battery; or 2) your car's quiescent current is high and flattened battery; or (again) 3) some combination.

if 1), then you might want to recover this battery to allow you to determine if your car has a fault (eg. boot light stuck on) before you invest in a new battery and have same issue.

if 2), then since battery current has been low, then 3 weaker cells have been reverse charged by stronger 3 cells. If this current is small, then recharging your battery will re-reverse these cells and battery may be saved. Some have thought that sulfation may have occurred where lead sulphate crystals have reduced surface area of your battery plates. Perhaps: a flat battery has 2 plates of PbSO4 but it takes time to make lead sulphate crystals that are hard to dissolve. Therefore charging these cells will be fine.

Rational thing to do is to replace battery, but if you have 2 cars and are interested in spending some time you might like to jump start car and go for a drive - perhaps to a shop to buy another battery just-in-case?

You alternator and regulator will have no problem recharging your battery - they run your car headlights at night with are typically 5A each, and a alternator can produce at least 70A (I think mine is 100A).

Answer 8

Yes, it is worth trying to charge it. However it might be worth you purchasing a charger if this scenario is likely to play out again in the future.

TLDR - Try charging the battery it is probably fine. Disconnect the battery from the car when not driving it for a week or more. Consider buying a good battery charger to recover the battery if you forget to dicsonnect it.

The Tool Long Version - Some models of car will drain a perfect battery to near dead in 4~6 weeks while left parked up. This is a fault in the design of the car, not a problem with the battery. It could also be a repairable fault with the car if it suddenly starts happening when it never did before. I had an old Jaguar XJ6 (x300) that would drain a perfect 120AH battery to stone dead in about 5 weeks. This was normal for that make and age of car. Nothing is wrong with the battery when this happens (although it may age the battery rapidly it it happens often).

When my battery was really flat it would only register a few volts. If it was only a little bit flat (after 2~3 weeks) then I would be able to get the car started. If I was unlucky I would get the car started and then the auxiliary drive belt would break under the strain of running the alternator hard to charge the depleted battery. To avoid this I either disconnected the battery when leaving the car more than a few days or when I forgot about it I made sure to charge the battery from a mains charger before hand.

I spent ~£60 on a Halfords Advanced/Smart Charger that could charge the 120AH battery for my car and the much smaller (40AH?) battery of my partners Ford KA. Even from near dead this unit was able to charge my large battery back to a working state. I am sure it did nothing for the lifespan of the battery and it would be better to avoid completely discharging it but it was better than buying a new battery every couple of months just to make sure it was charged. At worst the unit would fail the battery after a 24 hour charge cycle, then I would leave it an hour to cool off and I would try again and the cycle would pass. This did mean I needed 24~48 hours of charging before I could confidently use the car but it only cost me the power to charge a battery each time.

I did replace the battery at one point to see if that helped. It did seem to give me another week before starting the car became difficult or resulted in a lost drive belt but it did not resolve the issue altogether. I replaced the alternator with a refurbished one and the issue persisted. It was only by either disconnecting the battery when a week or more of standing was expect or charging from the mains after 2+ weeks of idle time that I avoided the issue altogether. Driving around for an hour or two might charge the battery if it is a little low but it would take a long time to charge a battery that was very flat this way.

Answer 9

If you have a car where the battery dies after leaving it, try plugging a solar charger on the dashboard into the cigarette lighter. This has kept me out of trouble for quite a while. Note that the cigarette lighter must be the type that is still connected when the ignition is off. Nick B