Why does battery charge so quick, then level drop?

[NakedDog]

Hi folks,

Living here in Canada, I bring my batteries in for the winter (2 trolling/ deep cycle & 1 starting).

I just put them on the smart charger, as they were all around 75-80% charge. I put each of them on the charger and they charged to 100% very quickly - probably too quickly. Then I checked them a couple of days later and they were at 85% again, so I did the process again. I first tried charging them at 10amp, then I tried 2amp with the same result.

All 3 batteries are new (within past year).

Why is this happening?

 

[1fishbone]

Re: Why does battery charge so quick, then level drop?

What kind of battery charger?
Is charger for FOR deep cycle batteries?

85% = 10.2v
Or 85% using the battery chargers display?

 

[NakedDog]

Re: Why does battery charge so quick, then level drop?

This is the charger I have: http://www.canadiantire.ca/AST/brow...arger%2Bwith%2BTime%2BIndicator.jsp?locale=en

The battery percentage indicates 85%, and the voltage reading indicates 12.6v.

I use the 'regular' battery setting for the staring battery, and the 'deep-cycle' setting for the deep-cycle batteries, so I think everything should be ok in this regard.

 

[NakedDog]

Re: Why does battery charge so quick, then level drop?

Thanks 1fishbone.

...I've been doing some more research, and think what I'm encountering is the "false capacity", as indicated in the cut & paste below.

"False" Capacity

"... you have to be careful that you are not just measuring the surface charge. To properly check the voltages, the battery should sit at rest for a few hours, or you should put a small load on it, such as a small automotive bulb, for a few minutes. The voltages below apply to ALL Lead-Acid batteries, except gelled. For gel cells, subtract .2 volts. Note that the voltages when actually charging will be quite different, so do not use these numbers for a battery that is under charge."

From the charging table I have looked at, 12.6% is almost a fully charged/100% battery. I don't know why my charger indicates only 85%.

Can anyone confirm this or provide a better explanation?

 

[1fishbone]

Re: Why does battery charge so quick, then level drop?

There is a float function, maybe they need to float longer?
From what I have been reading about the new chargers is they need more time, they ramp up, then float, ramp up and then float.

I would leave them or one on the charger for a few hours, then use a load tester.

I also read the older chargers can lower the life expectancy of deep cell batteries.
I guess that's another 'lesson' I have to pay for!

 

[BoatNoobie]

Re: Why does battery charge so quick, then level drop?

12.6v should be a fully charged battery. No?

 

[fishrdan]

Re: Why does battery charge so quick, then level drop?

I checked them a couple of days later and they were at 85% again, so I did the process again.

Is this an "automatic" charger with a digital display? How long did it take it to go from 85% to 100%, 5-10 minutes, an hour or 2?

Mine do the same thing as yours. I can charge them to 100% from a heavily discharged state and when I go back a several days later, they will read 85% and quickly top off to 100%. I have found this to be completely normal for a good battery.

On my old batteries, after charging them to 100%, they would read 50-60% after a few days, and it would take them a couple hours to reach 100% again. They were bad and had internal problems causing them to discharge while sitting idle. I replaced them this spring and my new (good) batteries do the same thing that you are experiencing.

 

[bruceb58]

Re: Why does battery charge so quick, then level drop?

12.6V is a fully charged battery. What it doesn't tell you is if the capacity of the battery is still good. Buy a cheap load tester from Harbor Freight to see if the battery is still good. A bad battery that has low capacity will charge up quickly.

 

[GTBecker]

Re: Why does battery charge so quick, then level drop?

85% = 10.2v? According to most data I've found, 10.5v under load is fully depleted, so 10.2v is trouble. 12.6v or better (after the surface charge has been bled off) is 100%, loaded or not.

Here's one reference, among many. "State of charge, or conversely, the depth of discharge (DOD) can be determined by measuring the voltage and/or the specific gravity of the acid with a hydrometer. This will NOT tell you how good (capacity in AH) the battery condition is - only a sustained load test can do that. Voltage on a fully charged battery will read 2.12 to 2.15 volts per cell, or 12.7 volts for a 12 volt battery. At 50% the reading will be 2.03 VPC (Volts Per Cell), and at 0% will be 1.75 VPC [10.5v] or less. Specific gravity will be about 1.265 for a fully charged cell, and 1.13 or less for a totally discharged cell." http://www.windsun.com/Batteries/Battery_FAQ.htm

 

[RonR]

Re: Why does battery charge so quick, then level drop?

I think your best bet is to purchase a hydrometer.
This is a device that tests the acid in your batteries. it jsut a big tube the sucks up the acid and has calibrated lines. they are very inexpensive. they may be purchase at Sears, or most automative stores.
Don't get the one that has color indicators go to a battery shop and ask to see what a good one looks like.
I am sure they will be very helpful.
RR