battery charging question

[Donald]

Two marine batteries, both flooded cell.

1) Starting battery, has been sitting on boat since Oct, no onboard AC charger.

2) New deep cycle battery dated 3/10.

Charger, a Black & Decker 2/6/10 "smart" charger set on 6

Battery 1 took about 90 minutes for the charger to say "FULL".
Battery 2 took close to 3 hours to go to "FULL".

I would have expected battery 2 to take maybe 15 minutes since given its manufacture date, it was basically brand new and should have been very close to fully charged.

 

[Eddie]

Not necessarily Donald. Deep cycle batteries have much thicker plates and take a charge much slower.

 

[fsskier]

A sealed lead-calcium battery will retain nearly all of its charge for 6 months.

A lead-antimony battery can internally discharge at 1 percent per day, and be totally dead after 3-6 months.

All car batteries were lead-antimony batteries from 1930 till about 1970, when Delco brought out the first sealed lead-calcium batteries.

Probably more deep discharge batteries are lead-antimony as are Exides.. if a battery is built by Delphi or Johnson controls it is likely a lead calcium battery..

If you use an unregulated charger, you will find that lead-antimony batteries will not go much over 14.2 volts (technical types would say they act like a zener diode) at full charge, a lead calcium will go well above 15 volts.

 

[tonycarguy]

There are differences in self-discharge rates between deep cycle and starting batteries, but I wonder if there's more to it here. 90 min is awfully fast to recharge a battery @ 6A that's probably less than 50% full. I would suspect the battery is on its last legs. They tend to exhibit this type of behavior where their voltage rises quickly during charging which fools the charger into thinking it's full. In fact the battery is no longer capable of holding a full charge and will probably die in a few months.

Disconnect the battery from all loads then let it sit overnight and test its voltage. At 75F it should be 12.6-12.8. If not it's on its way to battery heaven

 

[Donald]

After sitting all night (no charger) the starting battery is 12.89 and the deep cycle is 13.14 as measured by a decent Craftsman DVM.

The starting battery seems spot on, while the brand new deep cycle seems high.

 

[brianl703]

The self-discharge rate is also affected by temperature. Colder=lower self discharge. That battery has spent most of it's time since it was last charged in fall, winter, and spring.

 

[tonycarguy]

Originally Posted By: Donald
After sitting all night (no charger) the starting battery is 12.89 and the deep cycle is 13.14 as measured by a decent Craftsman DVM.

The starting battery seems spot on, while the brand new deep cycle seems high.



13.14 for the deep cycle isn't that high. AGMs and SLAs tend to be higher voltage than flooded cell starter batteries. I know my UPS and lawnmower batteries were 13.15 when new.

The true test is measuring electrolyte with a hydrometer, but you can do this only with your flooded starter battery.

 

[JHZR2]

13.15V is not a correct voltage for a LA battery. It is not indicative of anything in and of itself, as the battery has a "surface charge". What we do know though is that the battery is not self-discharging at a rate to destroy the surface charge quickly, which is a good thing.

 

[1 FMF]

Originally Posted By: Donald

I would have expected battery 2 to take maybe 15 minutes since given its manufacture date, it was basically brand new and should have been very close to fully charged.


bat 2 is normal and was slightly discharged having been on the shelf for a short while, and the charger brought it back to 100%.

bat 1 is stratified/sulfated having sat in a discharged state since october, the charger says it charged but the battery is not at 100% capacity. if you put a capacity test on it, such as checking it's reserve capacity you'll find it comes up way short.

 

[friendly_jacek]

Originally Posted By: Donald
Two marine batteries, both flooded cell.

1) Starting battery, has been sitting on boat since Oct, no onboard AC charger.

2) New deep cycle battery dated 3/10.

Charger, a Black & Decker 2/6/10 "smart" charger set on 6

Battery 1 took about 90 minutes for the charger to say "FULL".
Battery 2 took close to 3 hours to go to "FULL".

I would have expected battery 2 to take maybe 15 minutes since given its manufacture date, it was basically brand new and should have been very close to fully charged.


Is the "smart" charger calibrated for starting battery and too high voltage for deep cycle?

I have an automatic, but not "smart" marine/deep cycle charger and it undercharges starting batteries on auto setting. Fortunately, there is a manual override.

 

[Donald]

Originally Posted By: tonycarguy
Originally Posted By: Donald
After sitting all night (no charger) the starting battery is 12.89 and the deep cycle is 13.14 as measured by a decent Craftsman DVM.

The starting battery seems spot on, while the brand new deep cycle seems high.



13.14 for the deep cycle isn't that high. AGMs and SLAs tend to be higher voltage than flooded cell starter batteries. I know my UPS and lawnmower batteries were 13.15 when new.

The true test is measuring electrolyte with a hydrometer, but you can do this only with your flooded starter battery.


A deep cycle (at least mine) is still a flooded cell battery. I can pull the caps and look at the battery acid. I assume like others have said that the deep cycle holds a surface charge longer than a normal starting battery.