## Battery running times

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myp71
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### Battery running times

How long would a 10ah and a 19ah (two different batteries)but both 12volts lead acid batteries last when using around 70 watts.<p>Thanks
Myp71
Ryan

bridgen
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### Re: Battery running times

70W at 12V = 5.83A<p>A fully charged 10Ah battery will deliver this current for 10 divided by 5.83 = 1.7 hours.<p>A fully charged 19Ah battery will deliver this current for 19 divided by 5.83 = 3.2 hours.

k7elp60
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### Re: Battery running times

David is correct on the discharge current.
However the lead-acid battery capacity is based on a 20 hour discharge rate. Which means the 20 hour rate for the 10AH battery would be .5A.
But since it is being discharged at 5.83Amps the the would be closer to 1.25 hours to a discharge voltage of 11 volts.
The 19AH battery normal discharge current for the 20 hour rate would be 19/20 or .95Amps. So at the discharge rate of 5.83Amps it would last very close to 2.5 hours to the discharge voltage of 11 volts.
These discharge figures were taken from a set of characteristic discharge curves for lead-acid batteries at a discharge temperature of 68 degrees F. Of course the discharge rate is assumed that the battery is fully charged before the discharge period.
Ned

skrallman
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### Re: Battery running times

For lead acid batteries, that amp-hour rating is usually cited over a 20 hour period. For example, 10 Ahrs/20hrs = 0.5A . If you drew 0.5A out of the battery, you would expect to get the full 10Ahrs out of it.
But, the capacity decreases when you put heavy loads on it, expecially for lead acid batteries.
Page 6 of this link to powersonic batteries has a nice graph of sealed lead acid battery discharge time -vs- discharge rate.
Quickly looking at the graph, it looks like 55 min for the 10Ahr and 2 hours for the 19Ahr.<p>Scott

natcsparky
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