% Depletion rate of Fully Charged Battery

J

Joni Lynn

New member
I've read through all of the battery related threads (I think), plus a tutorial I found in one of the threads, but I'm still needing some thoughts from some of you folks who appear to be very knowledgable about batteries.

I have a 24 DP-4 Dual Purpose marine battery, built by Exide. I bought it new and was told that it was sent from the factory fully charged. The stickers indicate in was manufactured in Mar 06, and shipped May 06. That's new ! When I got it home, I put it on my charger and it indicated the battery was at 70% charged. I charged it @8 amps on the Deep Cycle setting untill 100% charged. I did not install it on my C Dory, but left it set on the bench in the shop. About 2 weeks later, wanting to make certain I would be installing a fully charged battery, I hooked it up to the charger again. The charger told me it was 75% charged. I again charged it to 100%, starting @8 amps for a few minutes and then down to 2 amps for the remainder of the charge. I did not install it on the boat, but left it on the bench. 3 days later I hooked up the charger, and I was given a reading of 80% charge.

This is the second time I've had this experience within the last 2 months. I"m been given a new battery, but this last time, after having tested it at the place I purchased it, they said it tests out OK, and that it's the nature of deep cycle batteries to loose a percentage of their charge in that period of time. They offered to give me my money back, exchange for another again, or whatever, but they are convinced the battery is OK. The clerk even took another one off from the shelf, and it tested out the same.

I'm having a difficult time believing that a brand new fully charged battery is going to loose over 1/4 of its charge doing nothing but sitting on a shelf in a clean, dry environment in 60 degree weather. Whether or not it has maintained its cold cranking power (which is really all they were testing), shouldn't it stay pretty near fully charged in such a short period of time? Is that truly the nature of the beast?

And, second question: When I do put it on a charger (in the shop, not on the boat), is it best to do the 2 amp trickle or 8, or 12?

Thanks C Brats. Although I seldom post, I continue to be a faithful reader and enjoy this site immensely.

Paul aboard the JONI LYNN
 
Don't claim to be an expert but my experience as a liveaboard for many years with a heavy dependancy on batteries and charging hardware tells me you really shouldn't be that concerned with what the meters are telling you. Percent of charge on most common guages is an approximation. And batteries that have been sitting around for days or weeks will always show somewhat low for the first few minutes the charge is applied. Lead acid batteries discharge some when idle over time. There are other technologies that discharge at a much slower rate but just like everything else, you end up paying more for better performance. Just don't continually discharge the lead acid batteries under about 10.8 to 11 volts and expect them to last the length of the warranty. If there is a chance you are going to run them to discharge very often go to gel or agm.
 
I have heard something about not placing batteries on concrete floors cause the rebar? or something lets them discharge. the old guys around here say to store your batteries on a slab of wood. Is there anything to that? Are your shelves metal? John
 
I think the optimax are agm batteries. I used one on its' side on the floor of a boston whaler and it worked great. Pounded heck out of it and it just kept on working. But it was pretty expensive.
 
Paul,

If you have a digital voltmeter, you can measure the resting voltage. A fully charged battery should read 12.5 volts and a 50% discharged battery is 12.2 volts. Fully discharged is 10.8 or 11.0 volts. That 0.3 volt between full and half charge is not very much and you need a digital voltmeter to accurately check the voltage.

Fresh off the charger, the voltage will be higher.

For the longest battery life, don't discharge past 50%.
 
drjohn71a":2f23fcun said:
I have heard something about not placing batteries on concrete floors cause the rebar? or something lets them discharge. the old guys around here say to store your batteries on a slab of wood. Is there anything to that? Are your shelves metal? John
Click to expand...

This came up awhile back - bottom line is that since batteries have been being made with plastic cases for a long time, storing on concrete doesn't matter "The old myth about not storing batteries on concrete floors is just that - a myth. This old story has been around for 100 years, and originated back when battery cases were made up of wood and asphalt. The acid would leak from them, and form a slow-discharging circuit through the now acid-soaked and conductive floor." Do a google search on "batteries concrete" and you'll find dozens of reliable sources indicating that storage on concrete is OK with modern day batteries.
 
One other thought is if you have a wet cell, get a hydrometer and measure the specific gravity [ratio of water to acid ] of the electrolite. This is the best way to see the condition each cell and the overall battery.
Else, you have to run a true load test for a specific amount of time, checking the terminal voltage before and after, along with the current
that reflects the ampere-hour rating. So, a hydrometer is much cheaper; but, again only for the wet cell; i.e., the lead-acid battery.

There are many simple units out there that will give you a color coded status. You can get these at any auto parts store and there should be directions with each to identify what the floating bulb's position means.
 
The "Charger" indicator is fooling you. As noted above, if the battery is 12.6, an hour or two after charging it is fully charged (some batteries settle in at 12.5 volts). I also do not discharge a battery to less than 12.2 volts--which as mentioned is 50% discharge. If you routinely discharge to less than 12.2 volts, it will significantly shorten the life span of the battery. A battery is fully discharged (for all intensive purposes) at 11.8 volts!

A good 3 stage charger is the best. I use a 6 amp smart charger on my RV, and have a timer set to come on 2 hours a day. The 2 amp chargers are not good for the batteries--they are poorly regulated. In the long run it pays to buy a good 3 stage charger, and save the "Auto" type for occasinal recharges.

The lead acid battery may loose several percent a month--but not 25% in a week. There is most likely nothing wrong with your battery. Get the digital volt meter and learn how to use it.
 
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