Douglas Krantz - Technical Writer - Describing How It Works
Go to the Fire Alarm Home Page of Douglas Krantz -- Describing How It Works
Go to the Fire Alarm Operation Map Page of Douglas Krantz - Technical Writer
Go to the General Electrical Map Page of Douglas Krantz - Technical Writer
Go to the Fire Alarm Description Map Page of Douglas Krantz - Technical Writer
Go to the Fire Alarm Installing Map Page of Douglas Krantz - Technical Writer
Go to the Fire Alarm Maintaining Map Page of Douglas Krantz - Technical Writer
Go to the Fire Alarm Testing Map Page of Douglas Krantz - Technical Writer
Go to the Fire Suppression Map Page of Douglas Krantz - Technical Writer
Go to the Science Article Map Page of Douglas Krantz - Technical Writer
Go to the Writer Home Page of Douglas Krantz -- Describing How It Works

Ask the Technician

Douglas Krantz -- Fire Alarm Engineering Technician, Electronic Designer, Electronic Technician, Writer

N P Asked:

Hi Doug,

I recently had our fire/alarm system inspected. One battery tested bad, one marginal in the FACP load test. 2 batteries tested bad on the door holder power supply during the load test. All the batteries were replaced 5 years ago so I am needing to replace them all. It was a new company that did the inspection and they quoted me $25 each for a 12V 8AH battery. They also want $115 to install them. When I opened up the panels and looked at the existing batteries I see that I have some that are 12V 8F and some 12V 7AH, none of them are 12V 8AH.

Does it matter if I buy 8AH, 7AH or 8F? I am trying to understand the difference in last 2 digits of the model # and not getting a lot of help. Should they all be the same?

I am OK with the cost per battery but I am having a little heartburn over paying someone $115 to do a simple replacement of the batteries. UNLESS I am missing a step that I am unaware of? I believe I need to notify our alarm company that I am changing batteries and to put us in test mode. Then unplug and remove each of the old batteries and replace with a new one of same type being sure to match black/black and red/red connectors. Is there a reason why I shouldn't change them myself? I work for a non-profit organization so every dime we save is important.

Thank you for your time and expertise with my questions.



Douglas Krantz Answered:

Douglas Krantz wrote:

For starters, the batteries are 12 Volt batteries with either 7 Amp/hour capacity or 8 Amp/hour capacity. The letters after the 7 or 8 are just manufacturer model numbers. The batteries themselves are pretty much the same from manufacturer to manufacturer. The capacity just means an equivalent of "how much water the glass holds".

8 AH batteries do have a little more capacity than 7 AH. In the long term, however, there's very little difference between 12 Volts 7 Amp/hours and 12 Volts 8 Amp/hours.

As far as changing them yourself goes. Yes, you can change them yourself and save a lot of money.

On the other hand, these batteries are dangerous. I used one of the same size batteries you have to help start my truck the other week. Just accidentally plugging them in wrong can cause problems like destroying the fire alarm panel. (I've seem where this happened.) If you plug the batteries in wrong, or something else happens as the batteries are being replaced, you might have to buy a new panel; if the alarm company does this, they might have to buy you a new panel.

N P Asked:

Hi Doug,

I really appreciate the information and that you explained it in an easy to comprehend manner. I honestly didn't think I would hear back from you, so thank you so much for writing me back. I am still on the fence about changing them myself or paying them to do it. I know it's an easy install, but you have some great points about having them do the work.

I look forward to checking out the rest of your web site, and I am actually in the market for replacing our fire panel and alarm system (currently they are joined together, proprietary and 20+ years old) so I know what not to buy when we replace both systems. If you have any recommendations on what to look for with a new system, I would appreciate the advice.

Thanks again,


Douglas Krantz Answered:

Separate Systems
Don't combine the fire alarm system with the security system; combining never works well. Besides being harder for you to operate the systems when combined (just the buttons and other controls are more complicated), when there is a problem with one, there is a problem with the other.

In the long term, cost of servicing combined systems is a problem. When combined, it is more complicated for whoever services the systems, and that costs more.

The one size fits all is really one size fits no-one. You are better off with two different brands of equipment because each brand can specialize as either fire alarm or security.

Not Proprietary
All brands of panel are proprietary to one extent to another. The difference you need to look for is that there are at least 3 independent companies that can service and program whatever systems you use. Especially look for the ability to program the panel. If only one independent company can program the panel, you are stuck with whatever service they give, at whatever cost they charge.

Ease of Operation - Fire Alarm
Most people fail to look at how easy or hard a system is to operate. Their system may be hard to operate or easy to operate, but almost no one finds out until after the system is installed, and then they're stuck with whatever is given them.

Check with other system users around town. Go to them and ask their maintenance people to explain to you how to operate their system. If they have trouble explaining to you how to silence or reset the system, you will have trouble explaining the system to your volunteers and employees.

You will have a screen, but stay away from touch screens. Touch screens look nice and feel nice, but during an emergency all they do is require attention to the screen rather than paying attention to the emergency. Go with simple buttons instead.

For the fire alarm system, the controls should be intuitive. Without much training, most authorized people should at least be able to turn off the local sounder in the panel. The most important buttons for you are:
  • Reset - The button should be labeled that way.
  • Silence Alarms - It might say Silence Notification, Silence Signals, or some such, but it turns off the horns and strobes around the building.
  • Panel Silence - It might say Trouble Silence or ACK (Acknowledge).
  • Scroll Buttons - These should be easy to operate.

Ease of Operation - Security
These are always more complicated to operate. Sorry. That's another reason that the security system should not also be part of the fire alarm system.

Remember, it's not the installing company that needs to operate the system, it's your employees and volunteers that have to understand how to use the system. Check around town for how easy or hard the system is to arm and disarm. Pay attention to how to stop alarms and how to find out which doors are open, preventing the arming of the system.

 Get your free diagram showing supervision for Class B wiring

PDF Book
PDF of Make It Work - Conventional Fire Alarm Systems
PDF of Make It Work - Conventional Fire Alarm Systems

Douglas Krantz

Describing How It Works

View Douglas Krantz's profile on LinkedIn

Short Circuit
Free Subscription
I'll Send You the
Fire Alarm


How Does Class A Fire Alarm Wiring Work?-- Fire alarm systems save lives and protect property. Fire alarm systems also break down because... Read More

Just What Is a Signaling Line Circuit (SLC)? -- The SLC (Signaling Line Circuit) is another way of saying Data and Power Circuit. Along with added power to run the sub-computers and their input and output circuits, it's a computer data-buss ... Read More

How is a Buffer Relay Wired Into a Door Holder Circuit? -- Like a door stop, a door holder keeps a fire door open. When smoke is detected, the door holder releases, allowing the door to shut. The door holder looks simple and innocuous enough... Read More

How Does One Find a Soft Ground Fault? -- Normally, we think of resistance like that of a resistor. The amount of resistance is built-in; no matter what voltage is used to drive the electrical... Read More

Can a Magnet Really be Used to Test a Smoke Detector? -- Smoke detectors usually have two ways of being tested. Smoke (smoke particles in the air, or some sort of canned smoke), and magnets (the activation of an internal magnetic... Read More

Electrical Flow

On this website, most references to electrical flow are to the movement of electrons.

Here, electron movement is generally used because it is the electrons that are actually moving. To explain the effects of magnetic forces, the movement of electrons is best.

Conventional current flow, positive charges that appear to be moving in the circuit, will be specified when it is used. The positive electrical forces are not actually moving -- as the electrons are coming and going on an atom, the electrical forces are just loosing or gaining strength. The forces appear to be moving from one atom to the next, but the percieved movement is actually just a result of electron movement. This perceived movement is traveling at a consistent speed, usually around two-thirds the speed of light. To explain the effects of electrostatic forces, the movement of positive charges (conventional current) is best.

See the explanation on which way electricity flows at