Battery Replacement

[ifmdalvey]

I have 2 Sportsman dualpurpose DP27M batteries with a date stamp of May 2007. CA 850, RC 170, AH 100.
Since taking the boat out of the water in October, i have stored the batteries in my garage and fully charged both on 16 November. The following numbers are the discharge rates i have noted:

Battery, 16 Nov, 7 Dec , 28 Jan, 3 Mar

1 = 12.84v, 12.67v, 12.58v, 12.56v

2 = 12.67v, 12.43v, 12.28v, 12.26v

The question is:
Do the batteries need replacing? can you tell from the voltage drop? or is there some other measurement i need to be taking?

Thanks

 

[Maine Sail]

I have 2 Sportsman dualpurpose DP27M batteries with a date stamp of May 2007. CA 850, RC 170, AH 100.
Since taking the boat out of the water in October, i have stored the batteries in my garage and fully charged both on 16 November. The following numbers are the discharge rates i have noted:

Battery, 16 Nov, 7 Dec , 28 Jan, 3 Mar

1 = 12.84v, 12.67v, 12.58v, 12.56v

2 = 12.67v, 12.43v, 12.28v, 12.26v

The question is:
Do the batteries need replacing? can you tell from the voltage drop? or is there some other measurement i need to be taking?

Thanks

You can probably throw out your 12.84 reading because you still likely had a surface charge on the plates as 12.84V is technically over 100% charged for most brands of wet batteries.

That is fairly normal self discharge for a wet cell battery. If your garage is cool that is probably the reason it has been slow. The colder the storage temp the less self discharge there will be. The warmer the storage environment the faster the self discharge.

Wet cell batteriess can self discharge up to 13+/-% per month depending upon temperature. This is why my batteries are topped up in the fall and left on board all winter. I top them up maybe once or twice that's it.

Below is the voltage to percent charge parameters for Trojan wet cells. Based on this you're still at roughly 70-80% for both batts. Letting them sit at 70-80% can lead to sulfation so throw them on a trickle/maintainer charger for a few days and top them back up. Were both of these batteries in the same parallel bank, or one start and one house?

100% = 12.73

90% = 12.62

80% = 12.50

70% = 12.37

60% = 12.24

50% = 12.10

40% = 11.96

30% = 11.81

20% = 11.66

10% = 11.51

 

[ifmdalvey]

Mainesail

Both batteries were in a parallel bank and i would alternate which one to use for starting.
I also have a 100watt flexible solar panel that is connected into battery one.

 

[Maine Sail]

Both batteries were in a parallel bank and i would alternate which one to use for starting.
I also have a 100watt flexible solar panel that is connected into battery one.

Probably he reason you have two batteries acting differently. Unless of course they were not in parallel and fully charged when you took them off.

A combiner can be used to keep both banks topped up via the solar panel. No need to alternate starting if you run them in parallel anyway. Probably best to add an inexpensive third "reserve battery" so you can leave the other two in permanent parallel mode so they wear & charge more evenly and together. For now I would just top them up to 100% together and monitor their self discharge. They should go down more in unison. If they don't one batt is likely in worse shape than the other..

 

[ifmdalvey]

Thanks for all your help Mainesail, i should just come down and talk rather than cluttering the net.
So if i understand correct, give them both another trickle charge, keep them for this coming season and buy a combiner?, what is it and where do i get one?