Who This Checklist Is For
If you've ever been 36 hours from a deadline and realized the battery in your Allen-Bradley PLC backup is dead, keep reading.
This checklist is for engineers, system integrators, and maintenance teams who need to verify critical components—like solar battery chargers, V-mount batteries, or the backup batteries inside an Allen-Bradley small PLC—before a hard deadline. It's not theory. It's the exact process I use when I have to confirm something is right in under 48 hours.
There are six steps. Step 4 is the one most people skip. Don't skip it.
Step 1: What Are You Actually Checking?
Honestly, this is where most mistakes start. I've had clients call me in a panic because they 'needed a battery for the PLC'—and it turned out they meant a 12V battery for a solar charger rigged to power the panel, not the PLC's internal memory backup.
Write down exactly what needs to be verified.
In my role coordinating rush logistics for a mid-size automation distributor, I started requiring a one-line description. For example:
- 'Verify voltage of 12V deep-cycle battery for solar charger providing backup power to ControlLogix rack.'
- 'Check and replace CR2032 coin cell in MicroLogix 1100 PLC before shipment.'
If you can't say it in one sentence, you don't know what you're checking. Stop and clarify.
Step 2: Get the Right Tool (and Know Its Limits)
You need a multimeter. Not a 'fancy' one. A basic digital multimeter is fine—if you know how to set it.
The question everyone asks: 'What setting should the multimeter be on?'
The better question: 'What's the acceptable voltage range for this specific battery, and does my multimeter measure that accurately?'
Most people grab their multimeter, set it to DC volts, and take a reading. That's step 2a. Step 2b is checking that the multimeter is calibrated. Trust me on this one—I once chased a 'dead battery' for an hour because my multimeter was reading 0.5V low. The battery was fine. I was the problem.
Checklist item: Verify your multimeter is working by testing a known-good source (like a fresh AA battery). If it reads 1.5V to 1.6V, you're good. If it reads 1.2V, your tool is lying to you.
Step 3: The Actual Measurement (It's Not Complicated)
This part is straightforward, but the devil is in the detail.
- Set the multimeter to DC voltage. Most battery checks are DC.
- Connect the probes: Black to COM, Red to V/Ω. Red to positive (+), Black to negative (-).
- Touch the terminals. If you reverse them, you'll just see a negative number. No big deal—just swap them.
- Read the number. That's the voltage under no load.
But here's the catch: A no-load voltage reading only tells you if the battery is completely dead. It doesn't tell you if it can hold a charge under load.
Step 4: The Load Test (The Step Everyone Forgets)
This is the single most overlooked step. I learned this the hard way. In March 2024, 36 hours before a client's factory acceptance test, I approved a 'verified' backup battery for a CompactLogix system. The no-load voltage was 24.1V—perfect for a 24V system. Under load, it dropped to 18V. The PLC would brown out. We almost missed the deadline.
How to simulate a basic load test:
- For small PLC backup batteries (like a CR2032), you might not need a load test—they power memory only. But for any battery powering a solar charger or a V-mount system, do this:
- Connect a resistor or a known load that draws the typical current. For a solar charger battery, this could be the control panel itself.
- Measure the voltage again while the load is connected. A healthy battery should drop less than 5-10% under load (depending on the chemistry and age).
I've tested 6 different types of deep-cycle batteries for this application. Here's what actually works: if the voltage drops more than 15% under load, replace it. You'll save yourself a call at 2 AM.
Step 5: Check the Date Code (Batteries Expire, Even If They Test Fine)
I can only speak to industrial automation, but this applies everywhere. Most batteries have a date code stamped on them. Allen-Bradley doesn't make batteries, but the OEMs they use (like Panasonic for coin cells) do.
Quick rule of thumb:
- Alkaline batteries: 5-7 years shelf life. If it's older than 3 years, be suspicious.
- Lithium coin cells (CR2032, etc.): 10 years shelf life, but performance degrades after 5 years.
- Lead-acid (for solar systems): 3-5 years typical. After 2 years, expect reduced capacity.
Checklist item: What is the date code? If it's more than half its rated shelf life ago, schedule a replacement. Don't just rely on the voltage test.
Step 6: Document the Result (or You'll Do It Again Tomorrow)
This worked for us, but our situation was a mid-size distributor with multiple technicians. If you're a solo engineer, the principle still applies.
After you've checked the battery, write it down. I use a simple sticky note taped to the battery compartment:
'Battery checked [DATE]. Voltage: 25.2V no-load, 23.8V under load. Load test: PASS. Date code: 2024. Next check due: 2027.'
Why? Because the third time we ordered the wrong replacement battery for a solar charger, I finally created this verification checklist. Should have done it after the first time.
Common Mistakes That Will Cost You
Based on our internal data from 200+ rush jobs, here are the top three errors:
- Skipping the load test. I already covered this, but I'll say it again. We paid $800 extra in rush fees once because we shipped a PLC with a battery that passed a no-load test but failed under load. Replacing it in the field cost three times as much as replacing it on the bench.
- Forgetting the multimeter battery. Pretty embarrassing when you go to check a battery and your tool has a dead battery. Keep a spare 9V in your bag.
- Assuming a new battery is good. I've had batteries fresh out of the box with 50% charge. It happens. Always test new stock before relying on it.
One more thing: This checklist works best for Allen-Bradley PLC systems, but it's basically universal. The principles apply to any battery-powered backup system. If you're dealing with a V-mount battery charger for a camera truck, same logic. If you're checking a 12V battery for a sailboat solar setup, same logic.
As of January 2025, this process has saved us an estimated $8,000 in potential rework. 5 minutes of verification beats 5 days of correction.
