# Charging a Sealed Lead Acid Battery

Registered Users Posts: 19
Hi all,
I'm trying to calculate the time to recharge a sealed lead acid battery to 100%. For example if I have a battery at 100%, and I discharge 10A for 1 hour, will it take exactly 1 hour to recharge the battery if my charger supplies 10A of charging current? Or will it take 1.1 hours, 1.2 hours, etc. Is there a term for that? ("charging efficiency?") I've looked on battery datasheets and I can't seem to find anything to answer my question.
Thanks for any help.

• Solar Expert Posts: 4,141 ✭✭✭✭
Re: Charging a Sealed Lead Acid Battery

Pretty much, and my experience is from Flooded batteries, there is no correct answer. As batteries approach full capacity they can accept less current. You do get close to 1:1 - 1:1.1 correspondence in the 50%-85% with the charging voltage appropriate.
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• Solar Expert Posts: 1,925
Re: Charging a Sealed Lead Acid Battery
diego96 wrote: »
I'm trying to calculate the time to recharge a sealed lead acid battery to 100%. For example if I have a battery at 100%, and I discharge 10A for 1 hour, will it take exactly 1 hour to recharge the battery if my charger supplies 10A of charging current? Or will it take 1.1 hours, 1.2 hours, etc. Is there a term for that? ("charging efficiency?") I've looked on battery datasheets and I can't seem to find anything to answer my question.

It is up to you how much you put back. With flooded batteries, the more you put back, the more bubbling you get. So, by varying the amps you can vary the amound of energy that goes to bubbling and efficiency changes accordingly. The correct amount of bubbling is important to flooded batteries. Sealed batteries do not need bubbling, so you should get something close to 1 or slightly higher.

The energy efficiency is worse than amp-hour efficiency because you charge at higher voltages and discharge at lower voltages.
• Solar Expert Posts: 4,812 ✭✭✭✭
Re: Charging a Sealed Lead Acid Battery

What does the maker recommend for charge parameters? Since they are sealed you should not EQ for one thing and, secondly the charge rate should be lower than FLA to avoid too much gassing... the H and O2 have to recombine into H2O.

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• Registered Users Posts: 19
Re: Charging a Sealed Lead Acid Battery
westbranch wrote: »
What does the maker recommend for charge parameters?

Powersonic sealed lead acid battery. Constant current (max 22A) up to 14.4V, hold at constant voltage 14.4V until current drops below 750mA. Battery is 100% at this point.
• Solar Expert Posts: 134 ✭✭
Re: Charging a Sealed Lead Acid Battery

I don’t know if this is a universal formula but this is what the manual for Sun Xtender batteries says. The Sun Xtenders are AGM batteries. I believe that AGM batteries are considered to be “sealed lead acid”.

Time to Reach Full Charge = [(DOD/100) X Rated Capacity (Ah) / Rated Output of Charger (Amp)] + 2 hours
For example, charging a 100ah battery at 50% DOD using a 25A charger would take:
Time to Reach Full Charge = [(50/100) X 100Ah/25A] +2 hours = 4 hours
Note that this formula is approximate and the full charge state should be verified using the criteria: current drops below 0.5% of the rated capacity (0.5A for a 100Ah battery).
• Super Moderators Posts: 26,658 admin
Re: Charging a Sealed Lead Acid Battery

That is what I use... But I would suggest that the time would be 2-4 hour range... The deep cycled the battery, the longer the "tail" of the charging cycle.

Also, Concorde batteries are AGM sealed lead acid--But they claim to be "different" from other AGM batteries and are able to accept higher charging voltages (and currents) that other brands may not.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 19
Re: Charging a Sealed Lead Acid Battery

Another charger question.
This is what my battery datasheet says: "Limit initial charging current to 22A."
I'm looking at using a Xantrex TRUECharge2 40A charger. The reason for getting a 40A charger is because I want to sometimes power a load in addition to charging batteries.
However if there is no load, will the charger try to force 40A into the battery? I assume that would damage the battery since the datasheet says limit to 22A...
• Solar Expert Posts: 7,224 ✭✭✭✭
Re: Charging a Sealed Lead Acid Battery
diego96 wrote: »
Another charger question.
This is what my battery datasheet says: "Limit initial charging current to 22A."
I'm looking at using a Xantrex TRUECharge2 40A charger. The reason for getting a 40A charger is because I want to sometimes power a load in addition to charging batteries.
However if there is no load, will the charger try to force 40A into the battery? I assume that would damage the battery since the datasheet says limit to 22A...
Yep. Maybe. If the battery was totally dead, it could pull the full 40A. But since you will have some charge in it, it will draw less, and as it approaches full, even less. That's why it takes such a long time to complete the last 20% of charge.
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• Solar Expert Posts: 4,812 ✭✭✭✭
Re: Charging a Sealed Lead Acid Battery

As mike said, if the battery is deeply discharged the TC40 will attempt to put 40 amps into the battery. The acceptance rate is dependent on the battery SoC... If yours (TC40) is the same as mine, the display will show the Amps being delivered...

KID #51B  4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge, Hughes1100 Sat Modem
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
• Registered Users Posts: 19
Re: Charging a Sealed Lead Acid Battery

I am considering 13.5V to be 100% charged and 10.5V to be 0% charged. The battery will never be lower than 10.5V. (Actually it is a 24V system with two 12V batteries in series.) So given that the battery will be 10.5 minimum, I hope the "intelligent battery charger" will not over-current the battery.
• Banned Posts: 17,615 ✭✭
Re: Charging a Sealed Lead Acid Battery

Repeated discharge to 10.5 Volts (21) will seriously shorten battery life. Charging to only 13.8 likewise. Please read the battery FAQ's: http://www.solar-electric.com/deep-cycle-battery-faq.html
• Solar Expert Posts: 10,311 ✭✭✭✭
Re: Charging a Sealed Lead Acid Battery

coachdad nailed it with the formula, but bill is right that the absorb time can get extended with deeper cycling, especially with some other agm brands as their charge efficiency may not be as good as the sunxtender for lower efficiencies equal longer charge times for the same amps in.

as to the charger it may be necessary to be sure to place the additional load on it to keep the charger from pumping too many amps into the battery. this could result in overheating and warped plates to name a few so do not exceed the max charge rate to preserve your battery.
• Solar Expert Posts: 762 ✭✭✭
Re: Charging a Sealed Lead Acid Battery
diego96 wrote: »