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Old 15-07-2015, 09:49   #16
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Re: when to charge battery

I heard that if leaving the batteries unused for extended periods ie 5-6 months is best afte giving them a full charge measure the voltage of each battery and record then disconnect completely . Before using again re measure the voltage and hook up...I would have thought leaving them on full charge with a trickle top up was the best way but some people say this isn't so....
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Old 15-07-2015, 10:07   #17
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Re: when to charge battery

"I would have thought leaving them on full charge with a trickle top up was the best way but some people say this isn't so...."

The best way to store a battery is with a 3 or 4 stage charger, with a proper float mode. This will maintain a healthy voltage for long term storage.

Problems can arise from using crude trickle chargers that don't have a float mode, so they tend to overcharge the battery, with loss of electrolyte, etc.

The worst thing, though, is to leave them disconnected, so they self-discharge slowly, and get sulphated.
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Old 15-07-2015, 10:08   #18
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Re: when to charge battery

lead acid batteries loose 1/4 amp per day to the air, hookup or not. high humidity will increase this. an automatic low amp charge will keep them charged and keep them from sulfating. Sulfating is the death of a battery. they all sulfate, charge slows it down.
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Old 15-07-2015, 10:09   #19
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Re: when to charge battery

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Originally Posted by amoret View Post
Hi, I've read that I shouldnt let battery fall below 50% charge, but how do I know when it's at 50 %? Thanks
If your question is when to charge batteries, the higher the charge maintained, the longer the battery life. The batteries would prefer to be charged constantly, and kept at 100% charge. This might not be practical when cruising, but the fact remains, the less deep you discharge, the better.
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Old 15-07-2015, 10:18   #20
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Re: when to charge battery

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Originally Posted by Bacchanal View Post
I have been stumped by my battery not holding a charge. I have one house bank 12V 8D battery. It is too large to remove in the winter during layup, so I charge it with shore power for a week before putting her to bed. A few times during the winter I run a cord to the A/C and charge for a weekend. I have never, even when new, seen the battery at 13.6V. It is now 3 years old. I just went to Bermuda and back with it, but I was really nursing it along by not using much power. The charging voltage is at 14.4V. Is there a way to bring this back? Simple charging doesn't seem to do it.
A normal, charged, good battery at rest with no load will only be at maybe 12.45 volts... if that relates to what you are asking.
BTW, I've had 2 8D batteries go bad with an internal short at less than one year of age. Just a side note... hopefully an anomaly!
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Old 15-07-2015, 11:11   #21
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Re: when to charge battery

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Originally Posted by Bacchanal View Post
I have never, even when new, seen the battery at 13.6V.
And hopefully you never will. Well, not for too long anyway. The resting voltage of a fully charged battery (100%) is around 12.65. You should only see 13.6 during a charging cycle or immediately after charging while the battery is bleeding off the surface charge.
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Old 15-07-2015, 13:25   #22
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Re: when to charge battery

Are the charging voltage profiles and discharge voltages ( usage) the same for starter/traction batteries and deep cycle batteries, both flooded type?
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Old 15-07-2015, 14:10   #23
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Re: when to charge battery

AFAIK, yes. If they are all flooded lead acid batteries the charging procedures should all be the same. Length of time to charge and automatic voltage adjustment by the charger will vary by battery capacity and condition.
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Old 15-07-2015, 21:35   #24
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Re: when to charge battery

Come into the Light...It's wonderful here.

LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks
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Old 16-07-2015, 03:02   #25
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Re: when to charge battery

Neptune's Gear says you must wait "at least 1/2 hour" to test the voltage and smac999 says you must wait 24 hours. (time the battery is totally disconnected from any load)

Any documentation on how the time affects the measurement? 1/2hr is not so bad but 24 hrs is difficult for a liveaboard.
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Old 16-07-2015, 05:20   #26
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Re: when to charge battery

You need to wait for the surface charge to dissipate, if you ever notice right after charging the volts hang up at 13 plus volts, this is a false state of charge. I always went with an hour or so. Another quick way is to connect a 12 volt tool or light for a couple of minutes to remove this charge, Just reconnect your terminal if already on the boat and turn on a load for a minute.
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Old 16-07-2015, 05:55   #27
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Re: when to charge battery

A few things to consider..

Temperature - Temperature will affect how long you need to wait for the surface charge to dissipate. At 80F, 24 hours should be sufficient but some batteries such as GEL and AGM can take longer. If the battery was just recently equalized 24 hours will not bring you back to rested voltage. In colder temps the surface charge can hang on for days and weeks even in flooded batteries. Many installed charging systems chronically under charge batteries due to short absorption times due to "egg timer" type charger algorithms. This means your time on float, to get to full, takes significantly longer.

I have a number of AGM & flooded batteries that have been off charge now for at least 5 days to 7 weeks that I just measured at 12.73V to 13.03V. Shop temp has been running about 74F to 78F for the last month.

AGM

Odyssey PC-2150 = 12.94V - Off charge for approx 7 weeks
Lifeline G-31 = 12.92 - Off charge for approx 5 weeks
Northstar Slimline = 12.98V - Off charge for approx 8 days
Deka GEL = 13.03V - Off charge for 4 days
Full River DC335 = 12.99V - Off charge approx 5 days
Firefly G-31 = 12.93V - Off charge approx 3 weeks
Deka G-31 = 12.78V - Off charge approx 7 weeks


Flooded

US Battery G-31 - 12.74V - Off charge approx 10 days
Trojan SCS-225 - 12.73V - Off charge approx 7 days

*Measured with a NIST Calibrated Fluke 179

If you are setting the bar at 12.6 - 12.65 your batteries are simply not getting fully charged or they are very aged.. I see very few batteries run through my shop that have resting voltages below 12.70V. When every 0.1V is roughly = to 10% of capacity......

Here is an interesting image to ponder if you think using a generic scale of 12.6V - 12.65V is a full battery. The only guide for open circuit voltage is the one your battery maker supplies or suggests for that battery.

This is a 110Ah AGM battery 1:23 minutes into a 20 hour capacity test. As can be seen we have removed 7.677 Ah's and the loaded voltage is still 12.766V. This is the loaded terminal voltage after 1:23 minutes at the 20 hour discharge rate of 5.5A..... How much capacity would we be leaving on the table to consider this battery full at a 12.6V - 12.65V resting voltage....??? How much chronic undercharging would be occurring & sulfation would occur if we deemed 12.6V - 12.65V for this battery as a full battery..?



Bottom line is don't let your batteries drop below 12.1V - 12.2V under your normal house loads and you'll be doing okay. Trying to get an accurate resting open circuit voltage, while cruising, is tough.
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Old 16-07-2015, 10:20   #28
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Re: when to charge battery

Interestingly, I bought two new Interstate batteries last year. After charging over night and testing after an hour or two both read 12.45v. Ditto after running most the day in the boat. (powerboat) These were wet cells though.
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Old 16-07-2015, 10:32   #29
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Re: when to charge battery

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Originally Posted by Maine Sail View Post
A few things to consider..

Temperature - Temperature will affect how long you need to wait for the surface charge to dissipate. At 80F, 24 hours should be sufficient but some batteries such as GEL and AGM can take longer. If the battery was just recently equalized 24 hours will not bring you back to rested voltage. In colder temps the surface charge can hang on for days and weeks even in flooded batteries. Many installed charging systems chronically under charge batteries due to short absorption times due to "egg timer" type charger algorithms. This means your time on float, to get to full, takes significantly longer.

I have a number of AGM & flooded batteries that have been off charge now for at least 5 days to 7 weeks that I just measured at 12.73V to 13.03V. Shop temp has been running about 74F to 78F for the last month.

AGM

Odyssey PC-2150 = 12.94V - Off charge for approx 7 weeks
Lifeline G-31 = 12.92 - Off charge for approx 5 weeks
Northstar Slimline = 12.98V - Off charge for approx 8 days
Deka GEL = 13.03V - Off charge for 4 days
Full River DC335 = 12.99V - Off charge approx 5 days
Firefly G-31 = 12.93V - Off charge approx 3 weeks
Deka G-31 = 12.78V - Off charge approx 7 weeks


Flooded

US Battery G-31 - 12.74V - Off charge approx 10 days
Trojan SCS-225 - 12.73V - Off charge approx 7 days

*Measured with a NIST Calibrated Fluke 179

If you are setting the bar at 12.6 - 12.65 your batteries are simply not getting fully charged or they are very aged.. I see very few batteries run through my shop that have resting voltages below 12.70V. When every 0.1V is roughly = to 10% of capacity......

Here is an interesting image to ponder if you think using a generic scale of 12.6V - 12.65V is a full battery. The only guide for open circuit voltage is the one your battery maker supplies or suggests for that battery.

This is a 110Ah AGM battery 1:23 minutes into a 20 hour capacity test. As can be seen we have removed 7.677 Ah's and the loaded voltage is still 12.766V. This is the loaded terminal voltage after 1:23 minutes at the 20 hour discharge rate of 5.5A..... How much capacity would we be leaving on the table to consider this battery full at a 12.6V - 12.65V resting voltage....??? How much chronic undercharging would be occurring & sulfation would occur if we deemed 12.6V - 12.65V for this battery as a full battery..?



Bottom line is don't let your batteries drop below 12.1V - 12.2V under your normal house loads and you'll be doing okay. Trying to get an accurate resting open circuit voltage, while cruising, is tough.
Instead of waiting days or weeks for the surface charge to self-dissipate, my understanding is that you can dissipate it by drawing some current. 10A per battery would be ideal. 5 minutes will not use enough power to significantly affect the stored capacity (used 1 Ah approx), but will dissipate the surface charge.
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Old 16-07-2015, 23:04   #30
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Re: when to charge battery

Wet cell batteries need to be Equalized every so often depending on their use, depth of discharge and length of time sitting discharged. Most good quality 3 stage chargers have an Equalization mode. Equalization is a controlled over charge of the battery. This overcharging cleans the plates of sulphation crystals that build up on a partially discharged battery. The Equalization cycle must be performed on a fully charged battery and monitored closely. Best practice is to charge the battery, then using a Hydrometer measure and record the specific gravity of each cell. Continue monitoring and recording the specific gravity of each cell until there is no improvement in the readings. Most battery chargers that have Equalization modes have internal timers and will automatically shut off after 5 or 6 hours. Make sure your battery compartment is well ventilated because the overcharge will push the voltage to 15 volts or higher causing the cells to boil. Also make sure you have any equipment or loads sensitive to voltage spikes turned off. I usually turn off my battery switch when performing an Equalization charge. This only works for wet cells, however I have read articles about Equalizing AGMs but only Life Line brand batteries. If the batteries are cycled regularly it is recommended that you Equalize them once every 30 days. For the poster that said they were losing capacity, you might want to try Equalizing the battery. You should see some improvement.
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