How long to charge battery ?

[Wishiniwuzfishin]

I took the battery out of my boat and brought it inside my house when I winterized the boat last fall. I just checked the battery and it has an approximate 75% charge according to my hydrometer. The label on the battery reads:
620 MCA (marine cranking amps)
400 CCA (cold cranking amps)
80 Ampere hours
200 load test amps
My battery charger is a 30-40 year old 6 amp charger and I don't know if it is automatic or not. So I want to check it with the hydro again to make sure it doesn't overcharge. I was just wondering how long I need to charge @ 6 amps to get back to full charge. I'm figuring I need to put 20 amps in it (the 25% I need to get to 100 % charge=25% of 80=20amps). So I need to charge at 6 amps approx 3 1/2 hours. Correct?

 

[Yepblaze]

Re: How long to charge battery ?

Hydrometers and charge rates, that goes back to the stone ages.

I clip on the automatic charger and when it says full, I unclip the leads.

And I probably even have a hydrometer here along with a pile of chargers.

 

[rjlipscomb]

Re: How long to charge battery ?

I'm thinking... 75% charge???, go put it in the boat, start 'er up and go have fun.

Or, go buy a new automatic charger. Safer for you and the battery.

 

[FisherOfCods]

Re: How long to charge battery ?

I use the "Battery Tender Junior" I got for like 30 bucks. Red light=not ready, Green light=time to ride. It's idiot proof. Perfect for me!

 

[boat1010]

Re: How long to charge battery ?

I'm not sure there is a table to say how long you will need to charge the batteries to get them fully charged. If you insist on using the charger you have I would check them about every hour to see what the reading is. Every battery is a little different. Some will take longer than others. But like some of the others have mentioned I would get a good marine charger and it will drop to a trickle charge and maintain the battery that way.

 

[Fl_Richard]

Re: How long to charge battery ?

As it approaches full charge it will absorb less and less of the 6 amps. Just because the charger puts out 6 doesn't mean the battery will absorb 6. I'd go for 5 hours and test it.

 

[achris]

Re: How long to charge battery ?

Charge until battery voltage is 14.7....

 

[Texasmark]

Re: How long to charge battery ?

My version: Timing a battery charge with conventional low amperage consumer chargers is almost impossible to determine because the charge rate varies as a function of the charge on the battery; lower the battery higher the current. Obviously you don't get something for nothing so if you want to get the amp-hrs out of the battery you have to put them in. Also, just because a battery is rated at a certain value, doesn't mean that it provides suitable power for you through out the full amount of stored energy.

A company like Exide or some of the more sophisticated batteries probably have tables on their www showing discharge rates and available voltages at those discharged levels.

Additionally, depending upon the discharge rate of a battery, considerable energy can be recovered if the battery is allowed to stabilize after a high current run. Sometimes when you think you have discharged your battery, trying to start a cranky engine, you can let it sit for 15 min or so and try it again to find you have a second life in the battery.

The temperature compensated hydrometer is the most accurate measurement tool as it measures specific gravity of the solution which tells you exactly where the chemicals (in the fluid) are.

They are a pain and sometimes getting one can be a problem. Before the advent of the digital (readout) multimeter it was not easy to get an accurate reading (even with a Vacuum Tube Voltmeter.....reading the meter was the problem). But now you can with a DMM or DVM.

Before attempting to read the voltage, the battery must have time to come off the charge voltage (like achris mentioned) and stabilize. Usually I'll quit charging one day and check my progress the next day....if I'm not monitoring the charging current while charging which tells me immediately what I want to know.

For me a stabilized fully charged battery is 12.75 volts at a comfortable temperature like 75F. Likewise, If I haven't used a battery for awhile, I'll just pop the leads on it for a second and know if I need to boost it or not.

Mark