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I don't have a proper lead acid battery charger... But I own a small Yuasa 7Ah battery. I am using a 13volt 1.5A wall wart to charge it. And I have a volt-meter to check the voltage.

At what voltage should I take the battery off the charger?

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2 Answers 2

up vote 5 down vote accepted

See my stack exchange answer to "Lead Acid Battery Charger Design Factors" which relates, and follow the link there to the Battery University site which will tell you far more than you knew there was to know about lead acid (and other) batteries.

From the above answer note the quotes from the above website. Especially in this context

  • The correct setting of the charge voltage is critical and
    ranges from 2.30 to 2.45V per cell.
    Setting the voltage threshold is a compromise, and battery experts refer to this as “dancing on the head of a needle.” On one hand, the battery wants to be fully charged to get maximum capacity and avoid sulfation on the negative plate; on the other hand, an over-saturated condition causes grid corrosion on the positive plate and induces gassing.

    To make “dancing on the head of a needle” more difficult, the battery voltage shifts with temperature. Warmer surroundings require slightly lower voltage thresholds and a cold ambient prefers a higher level.

2.30 x 6 = 13.8V

2.45 x 6 = 14.7V

13.8V is the nominal voltage that many automobile systems operate at.
14.7V is higher than you'd usually meet but around 14.4V is common for "topping" mode charging which is used to equalise charge in series connected cells. See the Battery University site for MUCH more information.

If you charge to only 12.6V as several people have recommended your battery will not ever be at full capacity and will have a shortened life.

See also Safe operating area for different types of battery chemistry?

And also Can I charge a 12v sealed lead acid with an old wall-wart (not made for charging)?

And also Charging lead-acid batteries?

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I love battery University. –  Kortuk Aug 20 '12 at 12:53
    
I love Mongkok :-). [Non sequitur. May never see it ever again. So it goes.] D700 coming. Some compensation for Mongkok. Just as well I don't drink. :-). –  Russell McMahon Aug 20 '12 at 13:11
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Deep Cycle Batteries charge on 3 stages. Bulk charge, toping and float charge. During the bulk charge the current density Amper/ cm2 or Amper/dm2 it is very important. If the current is smaler than needed for the surface of electrodes the crystalin structure will occur. Sponge material is reversible, but cristaline material it is reversible and this is very important for PbSO4 too. After the battery gets charged 80% then the current decreased and during the floating is less than 1 Amper. The best choice is using a Smart Charger. The way a battery is used and maintained can change the battery life from 6 months to 7 years. Newer let a dischaged battery to rest uncharged, and discharging the battery at 50% before recharging can prolounge the battery life 2 to 3 times.

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