Security & Fire Protection Systems/alarm system battery replacement


my lo/bt alarm just sounded ..can I replace this battery myself? My alarm system also shows a window is open when it actually isn' much should I expect to pay to fix either or both of these problems...approximately , of course.

Hello Lucy, and thanks for your questions.

On the battery issue, yes you can replace it yourself for probably about $20. For the window issue, that could be caused by several things, so I can't estimate a cost there ... but at a minimum, figure one hour of a technician's time; figure at least $65.

To replace the battery, here's an article I wrote that will tell you all you need to know:

Your alarm system has a rechargeable backup battery that keeps it running when the regular power goes out. Manufacturers estimate that these batteries have a useful life of five to seven years, although in practice many last longer than this.

Backup batteries are supervised by most alarm controls, meaning that when the battery is missing, fails, or does not charge correctly, a trouble condition is generated. Depending on the system, the trouble condition is annunciated at the keypad, and/or transmitted to a monitoring center who in turn will contact the system owner.

While your system will still operate under AC power with a weak or dead battery, it’s a good idea to deal with the issue as soon as you can, for two reasons. First, if there is a power outage, your system will probably not work. Second, when a battery is weak, the charging circuit in the control tries harder to charge the battery. This consumes more power, and as a byproduct, generates heat. Now we’re not talking about setting anything on fire, but the additional heat can stress electronic components and shorten their lives. If this happens, it’s likely that the main board in the control will have to be replaced.

If you have a maintenance agreement with an alarm vendor, replacement is as easy as making a phone call. The battery may be even covered by warranty. On the other hand, if you own the alarm equipment or don’t have a service agreement, you can replace the battery yourself. Here’s how to go about it.

First, if your system is monitored, call them and let them know that you’ll be working on your system. Doing this prevents unwanted calls from the monitoring center, if your work generates alarm or trouble signals. By the same token, you must call them again when you’re finished, so that they’ll again pay attention to signals that your system generates.

Next locate the main control panel, which will usually be located near to the keypad, tucked away in a closet or the basement. Remove the cover.

In the bottom of the cabinet, you’ll see the backup battery, connected to the main board by a red and a black wire. Normally these wires have connectors that plug onto the battery posts. Take a look at those connections, which should be tight and clean. If you see an accumulation of chalky gray powder around the terminals, you may have to replace the connectors as well. That’ll depend on whether the old connector (after cleaning with an old toothbrush) is in good enough condition to re-use.

The next step is to find the battery specifications. Look at the hookup diagram on the inside of the cover. You’ll usually find the specifications there. If the diagram is missing or does not have the specs, you can get them off the old battery itself. Here’s what you’ll need.

There are three parts to the specification: voltage, capacity, and battery type.

The voltage is the easiest, and most alarm panels use 12 volt batteries.

The capacity will be listed in either ampere hours (abbreviated aH) or milliampere hours (abbreviated maH).  

The battery type refers to the chemical composition of the battery. It’s important to select the correct type because the charging circuit is designed for that type. The common types are Nickel Cadmium (NICAD), Sealed Lead Acid (SLA), and Gel Cell (GC).

With this information in hand, you can shop the Internet for a replacement. Perform a Google search for “alarm battery” or “DIY alarms.” You’ll get several vendors, each with a means to drill down to batteries. You’ll find several different brands as well. You don’t have to get the same brand that you had, but the specifications need to match. Voltage and type must be an exact match. The capacity can vary a bit. For example, if you have a 4 aH battery, a 4.5 aH battery will be fine. Just keep in mind that the higher the capacity, the larger the battery’s dimensions will be. While there’s usually plenty of space in the cabinet, getting an 8 aH battery to replace one that’s 4 aH will probable not fit in the cabinet.

Once you get the battery, replacement is as easy as unplugging the old one, and plugging in the new one. It will begin to charge immediately, and any trouble condition should clear within a few minutes.

I hope that helps!

Best Regards,


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Dave Neuweiler


The design and application of burglary and fire systems for homes and businesses. Helping alarm owners understand how their system works. Helping to troubleshoot false alarm problems. Questions about monitoring issues.


Over a quarter century in the industry. Experience in installation, service, and monitoring centers. Training manager for a national protective services company; director of education and training for a national trade organization for for alarm dealers.


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