# 12v sealed lead acid battery, recharge or replace?



## Tree (Nov 23, 2004)

Hi all, I have a 12v 4ah sealed lead acid battery for my home security system that needs to either be replaced or recharged. How complicated is recharging, and how can I tell if it would be safe to do so? Second question if I need to recharge it is how? I've never delt with these before.

The model of battery that is in there now is Casil CA1240.

Thanks in advance for replies. /ubbthreads/images/graemlins/smile.gif


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## Tree (Nov 23, 2004)

*Re: 12v sealed lead acid battery, recharge or repl*

Ok another question. Until I figure out what I am going to do can I just unplug it? Will it cause the alarm to go off?

Don't you love the fact that I am asking you guys (and girls) instead of trying to find the electrician that installed it. /ubbthreads/images/graemlins/blush.gif /ubbthreads/images/graemlins/grin.gif


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## Lynx_Arc (Nov 23, 2004)

*Re: 12v sealed lead acid battery, recharge or repl*

Most home security systems have a trickle charging circuit built in. If the battery came with it, it is most likely just worn out. How old is the battery?


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## Tree (Nov 23, 2004)

*Re: 12v sealed lead acid battery, recharge or repl*

4 1/2 yrs since it's been installed.


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## Lynx_Arc (Nov 23, 2004)

*Re: 12v sealed lead acid battery, recharge or repl*

sounds like it is just worn out. Most lead acid batteries on constant trickle charge seem to last around 5 years for what I have experienced. I am not entirely familiar with home alarm systems but my *guess* would be disconnecting the battery probably wouldn't set it off, perhaps you should try to consult the manufacturers website for information about replacing the battery first before attempting.

I had a friend whose parents had the alarm company come out to replace their battery at $40-50 and I saw one listed the same size/specification for about $14.00 at batterystation.com. I would also suggest checking home depot, lowes, etc for prices too. If you cannot find an exact replacement a slightly larger or smaller one of the same voltage should suffice with larger being longer runtime off of the battery etc.


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## RussH (Nov 23, 2004)

*Re: 12v sealed lead acid battery, recharge or repl*

Gell cell batteries on float charge do tend to last only about 5 years. Keeping them charged keeps the acid at it's strongest and the usual failure mode is for the plates to dissolve (positive plate, IIRC) in the acid. They don't last much longer (if any) on cyclic charge since they usually are left partly charged (often) and therefore sulfate. The other main failure mode is loss of water from overcharging - that can happen on float charge, also.

Your alarm is expecting you to have a back up battery and in fact has to have one to meet certain fire codes. It's not uncommon to loose your electricity when there is a fire, especially since the electrical system is often the cause. Most of them show some kind of signal when the battery isn't there. Mine for example has an LED that lights up (I don't recall exactly what it does). Anyway, I can tell when the power has been off OR if it is running on the backup battery OR if the battery is dead (run down, not necessarily DEAD). Obviously, your alarm won't work when your power is off (without the battery), including if your burglar disconnects your power (Hey, it happens!). 

Home Depot usually has them and any electronic place should, even Radio Shack, as well as electrical distributors since they supply the alarm installers.


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## Tree (Nov 23, 2004)

*Re: 12v sealed lead acid battery, recharge or repl*

Great info, thanks guys. /ubbthreads/images/graemlins/bowdown.gif /ubbthreads/images/graemlins/thanks.gif


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## Lynx_Arc (Nov 23, 2004)

*Re: 12v sealed lead acid battery, recharge or repl*

Thanks go as much to CPF itself, I doubt either RussH or I would have been able to help if it were not to this forum and its members inspiring us to hang out here.


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## Tree (Nov 23, 2004)

*Re: 12v sealed lead acid battery, recharge or repl*

I'm always thankfull for CPF. Hanging out here has taught me so much.

Ok, I got a new one at 5ah for $12 from my local Southern Electronics . Now what should I do with the used one? Is it not safe to just pitch in the garbage can?


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## Lynx_Arc (Nov 23, 2004)

*Re: 12v sealed lead acid battery, recharge or repl*

I would check around for recycling center and drop it by there. I don't think it is worth money but it is better than it ending up in the dump one day. Around here walmarts have recycling centers at some of them you can drop stuff off at.
You can also drop off regular batteries too. I saved all my dead batteries in a metal coffee can and plan to take em all to be recycled now I know they will take them for free.


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## TheSteve (Nov 23, 2004)

*Re: 12v sealed lead acid battery, recharge or repl*

For future reference charging a lead acid cell is actually pretty much the same as Lithium Ion or Lithium polymer, just with different cutoff voltages.
Cell voltage is a nominal 2.0 volts, standard charge voltage is 2.3 volts per cell or up to 2.42 volt per cell(3 hours max)
The lowest you should discharge a lead acid cell is 1.7 volts, any lower will shorten its life.
A standard 12 volt lead acid battery has 6 cells in it, so the charge voltage would be 13.8 volts, or up to 14.52 volts for 3 hours max)
You normally charge them same as Lithium cells as I said before, with constant voltage and current. At the start of the charge the current is usually limited to a fixed amount, as the voltage increases the charge current will be lowered so as not to exceed the maximum voltage. When the charge current reaches 5% or 10%(depending on the charger) of the original maximum charge current the battery is considered "full".


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## Doug Owen (Nov 23, 2004)

*Re: 12v sealed lead acid battery, recharge or repl*

[ QUOTE ]
*TheSteve said:*
For future reference charging a lead acid cell is actually pretty much the same as Lithium Ion or Lithium polymer, just with different cutoff voltages.


[/ QUOTE ]

While what's said about lead/acid cells following this is accurate, the above statement is very much not so, and IMO dangerous to boot. Charging Li cells is in no (useful) way like lead/acid and to think so risks serious consequences with Li cells.

While it is true that a current limited charge to a set voltage is the profile for Li cells at the start, it is critical that charging be stopped when current at the cutoff voltage is reached. "Trickle" charging is forbidden. Tolerance on voltage an order of magnitude or more critical.

It is, again IMO, dangerous to think of the two systems in this way. In general folks don't get hurt charging lead/acid cells, the same can't be said of Li. Proven prowess (or even dumb luck) with the former can still be a major bummer on the latter.

Doug Owen


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