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I'm charging a 6 volt battery that is practically brand new but I've been cranking a 35 Packard with it in the cold weather and have drained down about 50 %. I'm charging with a correct 6 volt charger on my front porch and its about 20 degrees outside. Does the cold temp matter? Also, how long should it take to charge it back up?

I think you are ok in the 20's but be warned. Not about the battery, but the charger. I had one split open on me in below 0 weather. Don't know how or why, but I do not use them outdoors in those temps anymore. Granted it was a cheaper plastic one.

Wow! That must have been interesting. Hopefully, you weren't standing anywhere nearby when it blew.

Was it under warranty?

Craig

Much depends on the type of battery (- Lead-acid, gel, spiral gel, 'low maintenance lead-acid, etc). If it is an Optima battery they apparently require a different type of charger. I have an Optima 6V but no charger (yet) so can't provide much advice other than it is different technology used in these types of batteries so charging rate (current and time taken) is different to standard lead-acid. Optima info at Optima Batteries

Possibly the 20degree temperature is not very helpful to a battery when charging as the chemical reaction happening inside the cells at a very low temp might be altered by the cold and not happening 'normally'. Also it just might charge quicker if warmer (chemical reactions speed up with temp increases)so suggest taking it somewhere warmer, but others might have a better knowledge of this than I do! If it's lead acid don't forget to take the caps off to avoid a possible explosion.

A 50% discharged battery will possibly take 10 hours to fully recharge but this depends very much on the type of battery and also the type / capacity of the charger. Did you judge '50%' based on cranking speed as it got flatter?

My charger tells you the % that is left, that's how I knew. I just saw the my title to the post said "carving" instead of "charging"

That would be interesting for sure if I was carving :)

Haha!! That's why I read it Packard0 . . . a good way of getting responses.I was wondering just how you were carving it.

My old lead-acid charger has LED indicators (Red-Yellow -Orange-Green) so similar setup, but I don't know how they'd equate them to percentages . . .probably as voltages. 6V or less might mean 25%, 6.3V maybe is 50%, 6.5V perhaps 75% etc. If yours has a meter with percentages then it will need to be based on a range but the lower limit could be anywhere between zero volts (- a totally ruined battery I would think) and say, 5.5V which is still a quite low reading for a 6V battery. All my experience has been with 12V batteries and a voltage below 11.5v is very low charge compared to 12.7 or higher as it should be.

For a lead acid battery with removeable caps on the cells the most accurate way to determine the state of charge is by the specific gravity of the electrolyte (sulfuric acid and water mix, nominally about 20%). Specific gravity is measured with a battery hydrometer. A fully charged cell of a lead/acid battery should have a specific gravity of 1.275 - 1.280. 1.220 - 1.225 is about half-charge and anything less than 1.175 might make a bulb glow but indicates an essentially dead battery.

Check each cell individually of course; if the specific gravity of one does not increase while the others do while charging, that cell is "dead" and the battery is kaput. Further charging will not increase this value above 1.280. Capacity (not voltage) of a lead/acid battery drops dramatically with very low temperatures and I wouldn't leave it outdoors, either just sitting or charging. I'd guess that at 20 degrees or so, if fully charged, it should still be able to start a car or crank for a short time but there won't be much reserve capacity.

My ancient Allstate charger has a meter to indicate the charging rate in amperes; it goes to a max of 10 (depending on the state of charge of the battery) and automatically tapers to near-zero as the battery reaches full charge. If the charge rate does not eventually taper off towards zero, the battery is not capable of holding a full charge.

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No, I didn't get to see the show. Hooked it up and left it for a couple of hours. When I went to check on it, I saw the meter showed it was not charging. Disconnected it thinking the battery was ready and thats when I saw the case was split. Luckily I didn't get shocked. The charger was an old one, but was rock solid for years before that incident. Since then, I do not charge in cold weather unless absolutely necessary. If necessary, the battery and charger get moved to the garage.

Well it was about -30F in my garage yesterday and there are 3 batteries on trickle chargers. It is not unusual to have a battery charger hooked to a battery at these temperatures and lower. If I have a dead battery in winter I usually bring it inside but not always and unless the fluid is frozen or it is otherwise unserviceable they will accept a charge at very cold temperatures. My charger has low and high amp settings and an auto shutoff when the battery reaches full charge I usually start to charge at a low 2-4 amps and then increase the amps to 10 as the battery becomes charged.
The old fashioned way and the best way to test a battery is with a hydometer as O_D suggested IMHO.

Dave, if anyone has great cold weather experience, my bet is on you! Though it was only 9 deg. F. here in NJ when I awoke this AM.

Just a couple of more comments and some precautions to take note of. If the sulfuric acid content is low enough (the battery significantly discharged) and the temperatures cold enough, the electrolyte can freeze. This can crack the case of the old hard rubber battery cases, probably less likely with the modern plastic cases. But if the case cracks, when it thaws the sulfuric acid will leak out and of course even though a low %, it is corrosive! Also, charging a frozen battery has been frequently reported to have resulted in battery explosions. So be careful!