18

Use the jumper battery to start the engine, then disconnect it and leave the engine running (with no current drain such as lights, heater fan, radio, etc). The car should charge its own battery to 80% charge in about two hours (assuming the battery and alternator are in good condition; the battery may be damaged by being uncharged for so long, but I've never ...


18

The cost has been addressed, but there's an underlying question: is the battery dead (i.e. it cannot hold enough charge anymore to start the car), or has it just been discharged? If it's just been discharged (e.g. by leaving the headlights on while the car's parked), charging the battery is the best option. If the battery is dead, you'll have to replace it....


12

Lead acid type batteries, such as this, like to be charged very slowly. Under 5 amps for many hours would be best. During fast charging the internals overheat and electrolyte can boil. Best to charge slowly if time allows. This type battery has its worst damage happen when it is stored discharged. The chemistry in this state is more acidic. This acid ...


10

IIRC, the Prius has a step down voltage regulator which charges the 12v battery from the main power. I'd bet this system is having an issue and is not charging the battery. As for the 12v battery. I'd bet the old battery (the first replacement?) is good, but has dropped in voltage below what the charger can deal with. To overcome this, you need a second ...


9

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 ...


9

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, ...


9

As long as it is not overcharging your battery, it will increase the useful life of the battery. The reason behind this is, as a battery sits, it loses power. Some of the electrolysis which goes on to make a battery work, also breaks down the battery. During this period, the battery goes through a sulfating period, where sulfur crystals grow on the lead ...


9

A @FredWilson says, you need to charge it slowly - either by driving it around or by using a trickle charger. If you can get a trickle charger with a 'maintenance mode', you can leave it permanently attached to the car and it will keep the battery topped up and stop it going flat in the first place. If possible, I'd also recommend finding someone you trust ...


9

12.45 to 11.94 in 6 days seems like a significant discharge. You should be able to leave your car for a month or longer and still have enough power to start. At your current discharge rate, I wouldn't be surprised if you couldn't start after 10 days. I would be looking at parasitic drain. Here is a guide. You can find YouTube videos also. Some ...


9

Why don't you connect it to the battery directly? Do you know, that mechanical contact with metal springs inside lighter plugs is not very reliable? It has relatively big resistance and will be heating during flow of such high current for a relatively long time. What can potentially result in melting surrounded plastic panels and even cause fire if you ...


8

The difference is smarts. A trickle charger provides a constant current all the time. It does not know whether the battery is charged or discharged. A battery tender is smart. It will charge the battery only when it needs charged. After it's done charging it will shut off and monitor the battery state. When it sees the battery get to something like 80% (...


8

It is nice that some people put complicated math here (which is mostly correct also) but IMHO there was no reason to complicate it so much. As a rule of thumb: IF battery can be recharged then it is always cheaper and more environmentally friendly to simply try to recharge it. (it costs almost nothing to try) However if the battery damaged due to discharge (...


8

Similar batteries are used for motorcycles, and many people don't use those very often at all. They sit in the garage for months at a time until the weather is just perfect for that 20 minute ride. Batteries that just sit in the garage loose their charge, and when the voltage gets too low, real permanent damage can occur. The situation is the same as ...


7

I don't know the exact model of the trickle charger, but would suggest against using it and getting an actual battery tender instead. The difference is, the trickle charger will continue to charge, but at a really slow rate. This means, you can over charge the battery and cause damage to the battery with it. A battery tender will keep the battery in tip top ...


7

I'm not going to tell you to try and utilize a battery charger to fix the issue as @MoveMoreCommentsLinkToTop has suggested in the comments, but it has been my experience when a battery has sat for an extended period of time with a constant power draw on it, the lead plates get sulfide crystallized over and will no longer take a charge. If it does take a ...


7

In a word: nothing. If a battery is completely dry, or has a lack of electrolyte which doesn't contact the bottom of the charge plates, then nothing will happen. Even if one cell of a 6-cell battery (typical lead-acid 12vdc battery) is dry, nothing would happen. The reason is, the electrolyte (sulfuric acid) allows connectivity between plates. If there is ...


7

On my car, the lighter (power) outlet is switched with the ignition, so it is not directly connected to the battery, so you would not be able to charge the battery through that connector if the ignition is off (and perhaps not if the ignition is on.) Perhaps, on very old cars, the lighter outlet was powered at all times, so could possibly be used to charge ...


6

I'll preface this by saying, I don't think using a laptop adapter to charge a car battery is the way to go. If it's your only means to get it done, do it at your own risk ... that said: If you can get your battery back to 12v using the 12v adapter, it should be enough to get your motor started. Then the alternator can take over and recharge the rest of the ...


6

Your 12v adapter would only be able to raise the battery voltage to 12v, but to charge a car battery fully you would need to raise the voltage to 13.8v. The 16v adapter would raise the voltage too high and could cause damage. A 4A maximum current would be fine and would not cause any damage, but you need a 13.8v source. Batteries like NiCd need an accurate ...


6

The story is a bit rambling, but it sounds like your son's car has a serious electrical problem. 3 batteries behaving well for a long time, and all having problems at once is not a coincidence. Take one of your batteries to a garage (or, better, a battery shop) and have them charge and test it. It is possible to damage a car battery by overloading or ...


6

The most effective way to charge an additional battery from a single alternator is by use to a Split Charging setup. You can buy kits from various sources and they are common amongst both campers, where a leisure battery is maintained and competition audio enthusiasts (ICE cars) whereby several heavy duty batteries to drive additional amplifiers make up ...


6

It is very important to charge back the battery as soon as possible. As per how fast does the alternator charge the battery?, it may take as much as 10 hours or more for the battery to be re-charged if it was truly fully discharged (which might not necessarily have been the case in itself, due to the potential Negative surface charge?). It is much cheaper ...


5

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 ...


5

Most likely problem is a stuck thermostat and a blown headgasket.


5

When you put two batteries in parallel they will share the charge among themselves. For example, if you connect two batteries together, one fully charged and one dead the resultant combination gives you roughly two 50% charged batteries. This is in theory of course because the fully charged battery will dump a hell of a current into the dead battery ...


5

If the outlet is directly connected to the battery then it should be possible. Make sure to connect the solar panel through a charge controller configured for the chemistry of you car battery, so the charging will stop as soon as the battery is full. This protects the battery and the cars electronics. Adding another load should be no problem, there is just ...


5

You shouldn't be shopping for a battery charger but for a power supply. A properly designed battery charger will have protection circuits that stop it frying batteries (and on a bad day, starting fires) just because the user set it to the highest charge rate. That will most likely make it useless for electrolysis. On the other hand, if you tell an ...


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.


4

The correct way to charge a battery is to apply a charging current of around 1.5-2 amps to a maximum electrolyte specific gravity, then to fully discharge the battery at a very low 1 or 2 amps, then to re-charge the battery at a low amperage again, then discharge at a very low amps again. This process should be repeated until the electrolyte specific gravity ...


4

As you have already said, place the battery on a tender. Fill the gas tank completely. This prevents moisture from accumulating in the tank. They also make fuel stabilizer (Sta-bil is a common one) that you can add to the topped-off tank. It's not really needed for 12 months of storage, but it's cheap insurance. Placing the car on jack stands will take the ...


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