Battery Charging

[SARGE]

Need some opinions (or facts) concerning charging a car battery. Say you have a dead battery (fully drained) but battery is ok internally, meaning it will take & hold a charge. You put it on a home charger and let it get maybe half-charged or enough to start the car. Now, some say once it's back in the car the alternator/voltage regulator will only keep the charge at the level it was at when you removed it from the charger. Others say the alternator/vr will charge it to full capacity. I can't get a definitive answer to this.

Also, opinions about using a 2 amp trickle charge (takes longer) or a 10 amp fast charge.

[doctorgonzo]

The alternator will charge it fully, assuming the battery can take the charge. After all, when you jump a dead battery, the battery will be fully charged after driving around for 15 or 20 minutes.

[reboot]

Trickle chargers are used mainly to keep a charged battery charged, while in storage. I put the motorcycle battery on trickle all winter, with no ill effects. A 10 amp charge will simply charge it faster, so you can put it in the car sooner. Usually no harm done, providing you don't have any dry cells, or any dead ones. Beware that a quick charge at 10 amps can cause the electrolyte to boil, which is OK, just don't get any on you.

[SARGE]

Originally posted by reboot Trickle chargers are used mainly to keep a charged battery charged, while in storage.

So a trickle isn't recommended on a drained-down battery, mainly because it would take forever to fully charge? Someone said that the slower you charge it, the better.

[LawyerRon]

The alternator will charge the battery to full charge, assuming the battery is OK. Go with the 10 amp charge, get it running, then let the alternator fully charge it in 15-20 minutes or so.

[bob]

SARGE a car battery is not a deep cycle like a marine battery. If you let it drain to zero you will never to get it to recharge back to full with trickle or fast charge.
It will recharge but the reserve capicity will be lower - ie you will not be able to crank for as much time each time you drain it to the end.

[not important]

Try to charge the battery to a full charge with the battery charger. The alternator will charge it to full capacity after the car is running, but it is a little hard on the alternator. Newer vehicles are very demanding on the electrical system, which is supplied by the alternator, and it works the alternator very hard to run the vehicle and charge the battery all at once.
Any size of battery charger will charge the battery. A good slow charge is the best for the battery.

[HAL9000]

Bob is right... car batteries aren't designed for a full discharge, rather they are meant for a short burst or light usage, then charging. 2 Amp is fine, but ya.. will take forever.. but if it will turn the car over.. let the alternator do the rest.

[morriswindgate]

I read one time that it takes a drive of 26 miles or the equal engine runtime, just to recharge the amount of drain that it takes to start the car.
THe best way to charge this battery is to charge it at the 10 amp setting until the charge rate drops to below the 2 amp rate and then switch to that rate until it drops below 1 amp on the meter. The battery should be between 14.5 and 14.8 volts when fully charged.
JUst take precautions for gassing as it will put out a lot of hydrogen since it was fully discharged and make sure the water level is good before and after charging.

[bob]

Car bateries are 12 volts so a charge of 13.5 volts (ten years ago) was standard. I do not know the charge rates today but is the amps that count.

As for amp charge, my truck's alternator may be able to charge at 100 amps - I need to check.

[bailey]

if I remember right a lead acid cell fully charges is 2.2 volts

some altenators are as low as 25 amps, and some are as much as 125 amps, normal charge rate voltage is anywhere from 14.0 16.0 volts depending on the state of the regulator.

there will be no more wear on a altenator running at full amps for 10 years, than one running no amps for 10 years.

the altenator is completely solid state, the only wear will be on the slip rings brushes

[bob]

2.2 X 6 cells is 13.2 so 13.5 charge sounds like it still applies.

Hi balley.

There is other wear that applies on an alt that matters over 10 years - it is the berrings.

When I was poor I never replaced an alt - just the brushes and berrings but now the V regulators are built in. I just buy new at the first sign of a problem for any part on my ONLY (car) truck.

[morriswindgate]

9.4. How long does it take to recharge a good battery?

When a battery is discharged, the same amount of power has to be replaced. However, some of the power is converted to heat and lost due to the resistance in the cables, connectors and elements within the battery. For most SLI batteries that are discharged less than 10% of their full capacity, an estimate of time is amp hours to be replaced divided by 90% the current output of the charger. For example, a 40 amp hour battery with a 5% discharge would require approximately 2 amp hours to be replaced. Using 5 amp charger, it would take approximately .44 hours (2/(.9x5)) to recharge the battery. A 10 amp charger would take approximately half the time or 13 minutes. For batteries that are deeply discharged battery, an estimate of time is two times the number of amp hours to be replaced divided by the current output of the charger. For example, a 40 amp hour battery with a 95% discharge would require approximately 38 amp hours to be replaced. Using 5 amp charger, it would take approximately 15.2 hours ((38x2)/5) recharge the battery. A 10 amp charger would take approximately half the time or 7.6 hours.

I messed up the voltages I listed are with the vehicle running as I have one of those Battery/Alternator testors. With the vehicle off the voltage on a fully charged battery will be 12.6 - 13.2.

[Karnevil9]

The alternator will charge the battery to a full charge regardless of how much it was charged up by the battery charger. That is providing that the alternator and regulator are working correctly and you will have to run it for a while.

The way I remember the trickle versus fast charge. Trickle is used if wish to charge the battery and not babysit it. Overnight for example. There would be little worry of overcharging and boiling off the water, or stirring up explosives gases. A fast charge would be used if you needed the battery charged in a hurry and you would be near by to check on it periodically. I don't remember ever having to charge a battery that had zero voltage, so I don't know if that would still apply under those circumstances. If the battery is out of the vehicle, don't let it sit on a concrete floor, as it will discharge the battery. Place it on a piece of wood or plastic.

[lil Jimmie]

The battery on the concrete floor thing is a myth well part of it anyway, it won't discharge the battery any more than if it was on wood or cardboard, but it might ruin the concrete floor. With older batteries this was true, but with the polypropylene used in modern battery cases they don't have this discharge effect. And with the cooler temps of the concrete it may actually make the battery last longer as it will dissipate the heat that develops when charging.

[bob]

Here is the best link I can find.
http://www.magnacharge.com/mchg_all.htm
"/Automotive, or SLI (starting, lighting & ignition)
SLI batteries are commonly used to start and run automobiles, where a very large starting current is needed for a short time. SLI batteries have many very thin plates with a large surface area, designed to be discharged no more than 1 to 5% from full charge. These can be damaged quickly if deep cycled. /"


If you need to put a regular car battery on a charger it is probably already damaged and over drained.

Buy a new battery.

[bob]

Originally posted by lil Jimmie The battery on the concrete floor thing is a myth well part of it anyway, it won't hurt the battery one bit, but it might ruin the concrete floor.

Actually the difference in tempture MAY internally wear the inner lead plates at different rates. So when you recharge that battery - which would need to be done because they discharge even with out use - then it will not evenly recharge.

[Karnevil9]

Thanks for setting me straight Lil Jimmie, and that was an informative link bob. It is true that you learn something new every day. I must have had a lot of crappy batteries that happned to be on concrete floors

[glc]

In my experience, the best way to charge a car battery is with a "smart" charger that will taper off the rate as it reaches full charge, then shut down automatically.

[SARGE]

Thanks for all the replies, fellers. I believe we all learned something. Some good stuff.