# Safe voltage for batteries?



## budgetprepp-n (Apr 7, 2013)

I keep a close eye on my battery voltage. I try not to let it get to low.
But with a lead acid battery how low of voltage can I let them get without any damage?
As it is right now I try and keep them at 12.4 or higher. If I run my refrigerator on solar
during the day I'm ok but if I leave it on all night it will go down as low as 12.3 
I have a voltmeter for my batteries in the kitchen so I know whats going on 
so whats safe range?


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## PaulS (Mar 11, 2013)

This depends on whether you are checking the voltage under a load or whether this is an "open circuit" voltage. Under a load the battery should never drop below 10.5 volts. To check the state of charge on an open circuit battery (nothing drawing power from it) you need to use a hydrometer. There is no "minimum" open circuit voltage because a dead battery will read 12 to 12.2 volts when it is dead. As soon as you put a load on it the voltage will drop to 6 or less.


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## paraquack (Mar 1, 2013)

Everything I've ever read was 11.88 volts, so your pretty safe. The site below shows 11.9 volts as discharged
but never discharge a battery more than necessary.
Battery Basics: A Layman's Guide to Batte | BatteryStuff Articles


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## 8301 (Nov 29, 2014)

On a standard flooded acid 12v battery 12.1v while resting is 50% charge, That's the point you want to avoid dropping under to maximize battery life and staying over 12.2v after resting 10 minutes is even better. 11.5 v is basically a totally dead 12v lead acid battery.... not good as far as battery life goes. Seriously, try to never dip below 12.1v or 12.2v resting voltage with a lead acid battery. Even better build your battery bank so you rarely drop below 12.0v (under heavy load) and check your water every month.

Deep voltage draining builds stultification on your battery plates.


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## PaulS (Mar 11, 2013)

When checking an automotive battery for capacity the minimum voltage during the test is 10.5 volts - if the voltage drops below that it will not start your engine. (that click, click, click sound). The test is performed with a draw that is 100% of the amp hour rating for 10 seconds. A 60 amp hour battery would be connected to a 60 amp draw for 10 seconds while the voltage is monitored. The lowest voltage is recorded. This is done with a full charge and after a period of two hours to rest after the charge. 

A complete battery discharge test is performed with a 10% of amp hour rating for a period of 8 hours with the battery voltage and specific gravity of each cell monitored and recorded. If any of the cells specific gravity drops below minimum or the voltage of any cell drops below the minimum the test is stopped and the battery is either repaired or discarded. (I used to do this testing on commercial and automotive batteries)

Sulfate forms on every plate as it is discharged. It is a natural part of the charge/discharge cycle. As long as the sulfate doesn't get exposed to air or sit for more than 24 hours it will return to lead when the battery is charged. If it is exposed to air or is allowed to remain in a discharged state for 24 hours the sulfate (lead sulfate) crystallizes and will not return to lead no matter how much you charge it. You can perform a "shock" charge which breaks the sulfate off the plate but you have still lost some of your capacity from the loss of plate area.

Keep the battery filled, keep the temps in a habitable range, and keep them charged and they will last about ten years with 80 - 90% of their capacity.


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