Technical UPDATE - How long can you safely charge a battery?

I started using battery tenders about 15 years ago when my o/t mustang would loose it's charge if I didn't drive it for a month. This past May 2019 I replaced the battery in my '47 because it failed a load test, but it would still start the car. The battery was dated March 2006. Last summer I had to put a battery in my o/t truck, that battery I had originally put in there in 2006 also. I still have the o/t Mustang, it's battery is from 2009 and still going strong. I'm a firm believer and the battery tenders have paid for themselves just in battery life, not to mention never having a dead battery when I want to take a car out.

 

This is what I don't understand, see this on the automotive forums, everybody wants to know what the "best" battery is, and they run about $200 these days but a battery charger is way too complicated, even if they are a $4 item at any yard sale.

 

Well there was this time that I jumped the battery from my Lincoln Pipeliner welder...don't keep it hooked up very long...
Danny,
It all depends on the charger but the chart that was shared gives a real good guideline for charge times. It takes awhile for the initial bulk charging...hours, not minutes

 

I misplaced or lost the manual for my battery charger years ago and although there is some information on the top of the charger, age and surface rust has rendered it unless. HRP

 

Danny, your charger is a 40 amp and a 160 amp charger. I assume you put it on 40 amp to charge your battery for 45 minutes and then drive for five miles. That “ should” have charged your battery enough to start your car again, if your battery is “good”. Considering that the battery should have already had some charge in it while setting under the bench.
If the battery was “ dead” under the bench and had been “dead” for a while, I assure you your battery is bad.






Bones

 

There are no settings, the only choice is charge or start, that's it. HRP

 

To answer the original question, how long you can charge the battery depends on the size & type of battery, and the rate of charging.

@Doublepumper posted a good chart that should help. What is the lowest setting on that charger you have HRP? You really need a hydrometer to monitor the charge level when charging a battery, but if the battery is sealed you're out of luck for that. You might try using a volt meter to monitor the voltage, but that is not a great way to gauge the charge level. If your charger has a amp gauge on the panel that shows the current draw you will notice that when the charge level is low it will draw full current, so if the charger has a 10 amp setting you will see the amp meter showing a full 10 amps. As the charge level comes up the current draw will go down, so you'll see the amp gauge needle going down to reflect this. Since you can't access inside the battery a hydrometer, then watching the amp gauge is your next best method of observing the charge level of the battery. When the current drops all the way off it would be a good idea to disconnect the charger, or if it has a lower setting of say 2 amps, set it to that for awhile. You could leave it on the 2 amp setting for a long time, days, before it will hurt the battery, and then the worst thing that will happen is it will evaporate the acid in the battery and shorten the life unless you replenish it with water. A regular lead acid battery that is sealed can often be unsealed and opened up to add water, it just depends on the brand and how they built it.

The battery explosions that others have mentioned, 2 things will cause that. The first is an ignition source. Batteries will exhaust a hydrogen gas when being charged. If there is an ignition source close by that can lead to an explosion. Otherwise the gas will dissipate into the atmosphere. If however the vent on the battery is plugged, with no place for the gas to go, it could explode just due to the pressure build up inside the battery. There are 2 types of sealed batteries, those with a vent and those without (those without are the type you can mount in any position, usually AGM type batteries). If it is not an AGM battery than it will have a vent, it just doesn't have any way for you to add water to top if off.

 

That type of charger is intended for a production shop, it will allow quick charging of a battery, or jump starts, to get a customer going, but it's probably not the best for battery health, a slower charge will allow a deeper charge without over charging or heating the battery. Still, the amp gauge on the front will tell you the state of charge by how many amps it takes when charging. Though with the scale of that gauge it will be difficult to tell when it is getting to full charge. That charger is good for getting you going in a short time when you're in a hurry, but I'd invest in an inexpensive charger with a lower charge rate when you have some time to let the battery come up slowly.

 

Ahhh, “ dump” people?
I’ve been dealing with automotive batteries now for near 60 years. 33 of those years, I maintained a fleet of vehicles, some of which had six batteries. Some were constantly on chargers some not. The ones that were on chargers would hide battery problems, making problems difficult to find.
During that time, I guess I saw about anything a battery could do. Including a rather large(100 lbs) battery that was in relatively good shape develop an internal short and start “cooking” itself. That’s kinda scary!





Bones

 

I’ve got a charger similar to Danny’s, but mine has a 2 amp also. But even on 40 amp setting as the battery comes up the amp gauge will cut back to nothing. I then remove it.
While the 2 amp setting is “ better” for charging a battery, 2 amps takes a looonnng time if you are charging two large motorhome batteries. So I usually use the 40 amp setting.
My charger also says automatic on it, so it may be different than his.





Bones

 

Alternators are designed to keep the vehicle's battery or batteries in fully charged condition. They are fully capable of taking a low battery up to fully charged. But like mentioned it does make the alternator “ work” and just like batteries, the more you “work” them the quicker they will fail. But that’s true with anything mechanical.
A lot has to do with the age of the alternator and temperature . Heat is hard on all electrical components.






Bones

 

I noticed I don't seem to have many problems with alternators, since I started changing batteries when they get to be 5 years old. We have a lot of cars, and have had a lot of cars for many years, so I probably see this differently than some folks.

 

Any of us older geezer's, that ever worked in a gas station or a wrecking yard, will remember these cool dependable monsters. I have had this one for over twenty years, it was given to me by a good friend that had it for over twenty years before I got it. It weighs every bit of 60 pounds, ( heavy winding's in it ). Its rugged, built like a tank, and it has never failed me, and all of it works.
" Everything old is new again "

 

Yeah, 2 amps will really take a long time to bring up 2 large batteries, but if you have the time, once they've come up near full charge, then switch it to 2 amps and let it finish them that way.

I've had my battery charger for probably >40 years, it has a 6 volt 6 amp setting, and 12 volt - 2 amps or 6 amps setting. 6 amps takes a while, but will bring up a weak battery enough to get the car started, and then the alternator can take it from there. But if I have the time I will start the charge cycle on 6 amps, and when the amp gauge shows the current draw drop off to next to nothing I will switch it over to 2 amps and then let it slowly come up the rest of the way.

 

A defective battery can ruin an alternator, and the reverse is also true.

For charging, it's mostly a matter of "sizing" or matching the charger to the AH rating of the battery being charged. This is why the classic automotive battery charger, the kind that Sears or Monkey Wards and everybody sold for decades, were 6 to 8 amperes. It's possible to ruin a battery with these but it takes a dedicated effort.

About 10% of the battery ampere-hour rating (Not CCA) is a good compromise rate of charge. Slow enough to be a thorough and deep charge, though fast enough to reach 100% or near enough overnight. The "dumb" chargers are unregulated but the transformer (and ambient temperature) limits the end state charge voltage. In the pic above, notice it says max end voltage of 8 or 16 volts. If you play around with them and monitor the voltage and/or current you can get a feel on how this works.

The battery will draw about as much current as you can provide it. A 40 amp charger will get you going in a hurry, maybe a half hour or so, at the risk of warping plates due to excessive heat. As the battery accepts the charge, the current tapers off, and the voltage rises. On the other hand a wall wart will charge up a battery too, but it might take a week, and the battery will be outgassing for days. Moderate outgassing of the cells is actually a necessary stage of battery charging but it needs to be minimized. Hours, not days.

 

Jim I do the same on my Harley, new battery every other year! Since doing that, my charging problems have disappeared!
This goes back to what is a “ good” battery and what is a “ bad” battery. That depends on what you are doing with the vehicle.
Keeping an old battery in a vehicle, may save a person money on batteries, but will cost him more in charging problems and the inconvenience of possibly getting stranded.
I also “ move” batteries sometimes, depending on use of the vehicle





Bones

 

yup...I move batteries sometimes, also. When I get a new heap that I just want to get going, have fun with, and then sell, I will look around at the "keeper" cars and see if one has a battery that is getting older, and will need to be replaced soon anyways. I put the new battery in that car, and put the used battery in the new heap.

Letting any battery sit for a while without driving the car, is a really bad idea. At least put a charger on it once a month.

 

This is a great site if you really want to know

https://batteryuniversity.com/

 

No, if you really want to know AND have insomnia:

http://www.batteryfaq.org/

 

Sensory overload. HRP

 

Settings
40 amp charge
160 amp start.
If it were a snake it a bit you

 

That's what Danny said.......................charge(40 Amp) or start (160 Amp)

 

I get that, what I didn't know anything about is the charging times, like how long can I safely charge a battery. HRP

 

HOW LONG CAN YOU SAFELY CHARGE A BATTERY?
Until your Visa card is maxed out!

 

You can charge it for about an hour with that charger.

The normal thing to do is to see how many amps it takes when you start charging, or when it gets up to it's maximum charge rate, then stop charging when the current drops to half that amount.

 

Danny, I have a old battery charger that is made like yours and I was charging a battery and got side tracked and forgot about the battery when I remembered it had been on the charger for about 4 hours.

I stopped what I was doing and went to check on the battery , it was fully charged and has been in the coupe for over a year.

 

Good to hear that John, I have tomorrow off and I am going to take the battery out of the wagon and put it on the work bench away from everything and let it charge for a hour or two. HRP

 

http://www.batteryfaq.org/

I started reading this seemingly endless tutorial last night and sometime in the future I may read it through it's entirety, I thought War & Peace was one of the longest books I had ever took the time to read but it pales in comparison to CAR AND DEEP CYCLE BATTERY FAQ 2019 aka ( everything you ever wanted to know about batteries but was afraid to ask)

I have the battery on the charger as we speak, I'll check it in a hour and report back. HRP

 

LOL

I tried to warn ya....

 

GREAT INFO. ! Probably caused by the G-force bending the soft lead plates too close together.