Why do deep cycle batteries seem to lose charge so quick?

[lrdchaos]

I have two dual purpose batteries in my boat that I remove over the winter. With the batteries sitting in my garage for two weeks, that never gets below 45, I can hook them to my charger and it shows a voltage of 12.5 and 70 percent. Once I hook up the charger they are topped off in 30 minutes so they don’t take long to recharge. The same thing happens to my rv battery that is an Agm.

is it the charger, or do deep cycle batteries just slowly lose charge sitting?

 

[dingbat]

A fully charged battery should be 12.7 V or better. If you can’t get there, you have a charger issue.

Battery self discharge rates go up with temperature. Keeping them above 45 isn’t doing you any favors, but not the issue.

“Storing” the batteries at 12.5v is killing your battery.

 

[lrdchaos]

It is 12.7-12.8 when I remove the charger, but after a couple weeks of sitting they will read 12.5-12.6 when I go to top them off again.

 

[Scott Danforth]

you do realize that your charger may not be the right charger for the type of battery. each battery construction method needs a different charge voltage

here is just a sample.

State of Charge	Sealed or Flooded Lead Acid battery voltage	Gel battery voltage	AGM battery voltage
100%	12.70+	12.85+	12.80+
75%	12.40	12.65	12.60
50%	12.20	12.35	12.30
25%	12.00	12.00	12.00
0%	11.80	11.80	11.80

 

[dingbat]

It is 12.7-12.8 when I remove the charger, but after a couple weeks of sitting they will read 12.5-12.6 when I go to top them off again.

What are you using to measure voltage?

Should be 13+ when it comes off the charger. Surface charge will dissipate down to 12.7V

How old are the batteries? Mine are 11 years old and have sat since October. Dropped to 12.5

 

[lrdchaos]

I’m using the charger to measure voltage, I’ll stick my voltmeter on them next time.

They will show 13+ when I pull the charger off of them. It’s a smart charger that reads voltage and can charge wet cell, agm and gel. Batteries will likely be less than 6 years old, since the boat is a 15, and I don’t think it came with these batteries. They don’t take longer than 20-25 minutes to top off, so they may not be that low.

 

[JimS123]

Sounds to me like there's nothing wrong. If they drop below 12 in 2 weeks or don't reach 12.7 after charging, then you know the battery needs to be replaced.

 

[mike_i]

I don't see a problem. Dingbat is right on regarding surface charge. I'd use a voltmeter to read voltage and not rely on the charger's voltmeter.

 

[froggy1150]

Also dont set them on the ground. That will discharge yhem also

 

[JimS123]

Also dont set them on the ground. That will discharge yhem also

That was true in 1952, but modern battery technology has made that fact obsolete.

 

[froggy1150]

Dam jim.... now i feel old!

 

[JimS123]

Dam jim.... now i feel old!

Hahahaha.

Back then I was sittin next to Grandpa at the helm, so my guess is that I'm probably older than you are.

 

[Captain Caveman]

I used to pull the batteries and store them in my basement. Now I just disconnect all three batteries and leave them in the boat for the winter. My starter battery is 12 years old and going strong. The two deep cycles are about 3 years old, so the originals lasted 9 years.

 

[JimS123]

I used to pull the batteries and store them in my basement. Now I just disconnect all three batteries and leave them in the boat for the winter. My starter battery is 12 years old and going strong. The two deep cycles are about 3 years old, so the originals lasted 9 years.

I still pull the batteries out of the boats and lawn tractors, etc., and charge them monthly in the basement. One exception - an old classic car. It sits in the garage and never gets charged unless the car gets driven. I leave it in just in case we see a nice Winter day with the roads clear, so i might take her around the block. (I don't believe in running a car in place)

Anyway, I admit to not paying too much attention to the old girl. Last Spring I just happened to look at the date sticker and decided to replace the battery, "just because", not because it was bad.

It was a 19 year old Sears DieHard.