Duration for charging deep cycle batteries?

[TonyNoriega]

On my new (new to me) boat, which has a Dual Pro two-bank charger - 5 amps per side - connected to two group 27 12v deep cycle batteries, I would like to know if there is a way to know how long it should take to charge them. I ask because I started charging them 36 hours ago when each read 12.25 (approx) on my multi meter, and only got up to 12.55 after the 36 hrs(yes I waited about 2 hours after disconnect for the surface charge to dissapate).

Does this seem right to you guys? The batteries are 6 mos. old and fluid level is up to snuff. Thanks!

 

[Barnacle_Bill]

Re: Duration for charging deep cycle batteries?

Test your charger. Unplug the AC then disconnect all the leads going to the batteries. Situate the leads so they don't short out then plug the charger back in. Now check the voltage at each set of leads. They should read about 13.3VDC. If they don't you have a charger problem. A fully charged battery should read 12.66 volts.

 

[Silvertip]

Re: Duration for charging deep cycle batteries?

.11V difference in measured vs full charge is within 1% of meter error. That said, it should not take 36 hours to charge those batteries. I have a 6A Guest on my boat and it fully charges a deep cycle over night. The length of time it actually takes depends on how discharged the battery is to start with and the charge rate of the charger.

 

[TonyNoriega]

Re: Duration for charging deep cycle batteries?

Thanks for the help gentlemen....I'll see what I'm reading in the morning and then I'll do the recommended test of the charger. I sincerely appreciate your advice!

 

[Barnacle_Bill]

Re: Duration for charging deep cycle batteries?

.11V difference in measured vs full charge is within 1% of meter error. That said, it should not take 36 hours to charge those batteries. I have a 6A Guest on my boat and it fully charges a deep cycle over night. The length of time it actually takes depends on how discharged the battery is to start with and the charge rate of the charger.

My 3 bank 5 amp charger will charge overnight too.

 

[TerryMSU]

Re: Duration for charging deep cycle batteries?

I also bought a new-to-me boat this spring and my batteries took quite a while to finally get up to full charge. It seems like it might even have been 2 or 3 days. Now they charge up much faster. It sounds like you have the same issue I had. It might be what is called sulfation (if my memory serves correct).

TerryMSU

 

[wire2]

Re: Duration for charging deep cycle batteries?

It can be roughly calculated. If a battery is 600 amp hours and half discharged, it needs 300 amp hours from a charger to bring it back up. 5 amps at 12 volts for 1 hour is 60 amp hours, so theoretically it should be charged in 5 hours.

Realistically, the charge rate drops off as it approaches full. In 2? hours the rate drops to 2? amps and so on, effectively doubling the time to 10 hours.

 

[Boatist]

Re: Duration for charging deep cycle batteries?

When we pre fish the day before a tuornament with a single group 27 battery and come back by 2 PM we put on a 10 amp smart charger on the battery and it is never fully charged by 4 AM the next morning.

Voltage times the current is for Watts not amp hours.
5 amps for one hour is 5 amp hours not 60. Yes it is 60 watts.
Also no charger will charge at it rated amp as the battery reaches full charge.
Some multi stage chargers will do a good job of putting the charge back in faster but still do not charge at the full rated amps for more than about half of the charge. Some manual charger will charge faster but they will also over charge if your do not watch it closely.
Most charger I have seen on battery after 12 hours will only charge at about half there rated amps, so for a 5 amp charger your looking at 2.5 amps.
For Group 27 batteries I think a 15 amp or more smart charger is the best choice. It will charge faster so less damage from the battery being discharged for a long time.

 

[craig stevens]

Re: Duration for charging deep cycle batteries?

i recently learned that batteries that are allways charged slowly get a form fo crust. cant remember the name for it. i was having the same trouble so i used my 15 amp auto charger on full. fixed the problem

 

[gonefishie]

Re: Duration for charging deep cycle batteries?

Amp Hour is the storage rating, it really have nothing to do with the charge rate. The Amp Hour rating tells you how much amperage is available when discharged evenly over a 20 hour period. The amp hour rating is cumulative, so in order to know how many constant amps the battery will output for 20 hours, you have to divide the amp hour rating by 20. Example: If a battery has an amp hour rating of 75, dividing by 20 = 3.75. Such a battery can carry a 3.75 amp load for 20 hours before dropping to 10.5 volts. 10.5 volts is the fully discharged level. The only practical way to tell the state of charge is by how much current is going into the battery from the charger. My charger have a gauge that the needle normally start at 6-8 when first plug in, it drops toward zero as time goes by. I know the batteries are full when the needle hit zero.

 

[Boatist]

Re: Duration for charging deep cycle batteries?

A group 27 battery is about 100 amp hours. Some a little more and some a little less. If your charger put out a constant 5 amps then it would take 20 hours to fully charge.

However Since all on board charger I have seen are smart chargers and will not over charge but instead taper to 0 amps as the battery charges no way to tell exactly how long it will take. I would bet the average charge of a 5 amp charger is less that 2.5 amps durnig the bulk charging. So would take at least 40 hours to reach the 85 percent of charge. The Absorption and Float charge can take just as long. Another factor is how far discharged it was.
So I guess with a 5 amp charger will take a very long time if fully discharged and not damaged.