Keeping your world up and running.®

The right batteries keep test tool users in charge

December 2012

The Right Batteries

The Fluke Ti125 Thermal Imager for industrial and commercial applications ships with two field-replaceable, rechargeable lithium battery packs and an external two-battery pack charging base. You can add an extra battery pack.

There’s no time to waste: a failed circuit has shut down your plant.

Out on the job, you set up your test tool to take a reading and…nothing.

Dead battery. You did pack a spare in your tool bag, right?

Whether it’s a basic digital multimeter (DMM), a thermal imager, or a high-end portable oscilloscope, your handheld test tool is dead without its battery. That’s the simple truth. But designing the tool for the battery that works best is anything but simple.

Just ask Joe Swanzy, Product Evaluation Manager, and Ed Henry, Engineering Technician, at Fluke. Fluke tools are designed to work with their batteries as a team, with battery performance matched to the specific demands of each tool.

There are no “good” or “bad” battery technologies. Some, like zinc chloride or alkaline, are fine for “primary” cells that you use once and toss. For a tool that uses more power, rechargeable “secondary” batteries using nickel/cadmium (nicad), nickel metal hydride (NIMH), or lithium ion (lion) technology are the best choice. Even lead/acid rechargeables, using the same basic technology as a car battery, have their place. Each type has its advantages, and Fluke tools use just about every technology available.

Let’s take a closer look at the battery types and their best applications.

Zinc chloride: Low cost, but good enough for some applications

Before alkaline, zinc chloride was the battery that powered flashlights and kids’ toys. And it still makes sense for test tools like basic DMMs that draw little power and may receive intermittent use. It takes very little energy to power a DMM’s liquid crystal display, Henry points out, so these so-called “heavy duty” batteries can do the job. But start adding power-consuming features, like a high resolution display, backlight, or a flashlight, and you’ll need the added power of alkalines.

Alkaline: More punch to power more features

Alkalines have a higher energy density and deliver more power than zinc chloride batteries, and their slow discharge rate gives them a long shelf life. But Swanzy warns that expectations for alkalines have changed. Battery makers have changed their seal technology, and no longer guarantee battery storage performance from -40°C (-40°F) to 50°C (122°F). The new standard is -20°C (-4°F) to 40°C (104°F) for leaks, and replace them after a year, hot sun or not.

As Fluke designers choose the battery for a new tool, size is another factor they weigh. A smaller battery leaves more room for components and safety clearance. That’s why many Fluke DMMs use 9V alkaline cells - good for 400 hours of typical use in the Fluke 117. By contrast, the Fluke 289 DMM uses six AA alkaline cells to deliver up to 200 hours in data logging mode.

One way to improve battery life is to make smarter tools. The Fluke 381 Clamp Meter and Fluke 233 DMM both feature removable displays. If the displays are removed but receiving no wireless signals, they turn themselves off. Display backlights too shut down after a time to save power.

Lithium: When power is everything

Single-use lithium iron disulfide batteries are the best choice for some tools. They pack up to four times the power of alkalines. In the new Fluke 805 Vibration Meter, for instance, users who did not properly power off the device found that the AA alkaline batteries could potentially drain in hours. Fluke now ships lithium cells with the 805, and will send buyers a complimentary set of four AA lithium batteries to replace their original alkalines.

Rechargeables: The new game is lithium

Batteries you can charge and use again (secondary batteries) have been around since French inventor Gaston Plante developed the first practical lead-acid storage battery back in 1859. Modern lead-acid batteries are still used in some Fluke devices, such as the Fluke 732B Direct Voltage Standard and Fluke 1555/Fluke 1550C Insulation Resistance Testers. But especially for handheld tools, other battery technologies are a better fit.

Nicad: No thanks for the memory

“Memory” is one problem with nicad rechargeables. For optimum performance, they should be completely drained before being recharged, or they develop a “memory” that limits how much energy they can store. Another issue: the cadmium contained in the batteries poses an environmental problem. Once the standard for rechargeable compact batteries, Nicad technology is quickly being replaced by NIMH and lithium.

NIMH: A step up

Your laptop and digital camera are probably powered by nickel metal hydride batteries. NIMH has good energy density, handles applications that require high power delivery, and avoids memory problems. The nicad battery pack that once powered the Fluke 120 Series ScopeMeter® and Fluke 43B Power Quality Analyzer has been supplanted by a NIMH pack that delivers 50 percent more power.

“It’s still a viable chemistry,” Swanzy said. “There’s still a lot of support to retain that product.” But NIMH won’t work everywhere. Swanzy recommends against replacing alkalines, which are fully charged at 1.6 volts, with rechargeable NIMH AA cells, which reach a maximum of 1.2 volts. The voltage difference could affect the operating life of the product.

Lithium ion: Light and powerful

As test tool displays grow larger, with more detail and better graphics, they consume more power. Today’s rechargeable hero is the lightweight, powerful lithium ion battery. Lithium provides high energy density and is slow to self-discharge. The battery packs used in Fluke thermal imagers and the new Fluke 190 Series II ScopeMeter®, for instance, use lithium ion. The technology typically delivers a five-year operating life, Swanzy said. When lithiums reach end of life they can be recycled through Fluke (contact your authorized Fluke Service Center).

Lithium ion batteries are available in 9V but NOT in an interchangeable AA style. The lithium ion battery the size of an AA has two different voltages. The “14500” (its metric dimensions) delivers not 1.2 or 1.5 volts, but 3.7 volts; however, the L91 AA lithium battery provides 1.5 V and is the same size as the standard alkaline battery.

To maximize the life of lithium packs, Swanzy recommended discharging them to 40 percent, then recharging to a maximum of 70 percent. The chargers in newer Fluke tools are designed to optimize battery life. Still, lithium battery packs will eventually wear out. When they do, he said, users will be glad they bought a Fluke and can buy a battery replacement.

But the power of lithium cells demands careful design to ensure safety. When shorted or otherwise mishandled, lithium cells have caused fire. Today some cells have built-in circuit protection and other safety measures to prevent shorts or excess heat. Fluke battery packs have at least two levels of built-in protection for the user.

Of course batteries aren’t the only choice for powering test instruments. Test tools that may remain on the job and collect data for an extended period, like a power quality analyzer, can draw line power directly from the grid, making battery life a non-issue.

Your tool…you’re involved

Tools and their batteries come together in a system precisely tuned for the job they have to do. The tools are designed to help. Swanzy pointed out that many Fluke battery packs have a built-in “gas gauge” that shows their state of charge, and many newer tools provide a battery status reading.

But there’s another element key to the system: you, the tool user. Users need to understand how each tool stores and uses power, and take the steps necessary - by checking battery status and plugging in the charger or replacing spent batteries - to keep their tools job-ready.

You do have those spare batteries in your bag…right?

Battery Matchup
Category Power
(AA size)*
Full Charge Voltage (AA) Pluses Minuses Recharge Cycles (est)*
Primary (single use) Technology
“Heavy Duty”
1100 mAh   Ubiquitous
Low cost
Limited power N/A
Alkaline 2400 mAh Nominal 1.5 V Ubiquitous
Good power
Long shelf life
Higher cost
Can leak
Lithium-Iron 2100-3000 mAh   Max power
Extreme shelf life
Higher cost N/A
Secondary (rechargeable) Technology
Lead-acid N/A N/A Low cost for output Heavy
Less durable
Nickel-Cadmium 600-1000 mAh 1.2V   Memory
Heavy metal content
Up to 1000
NIMH 1200-2900 mAh 1.2 V Ubiquitous
Good power
Higher self-discharge 500-1000
Lithium Ion N/A AA size (14500) delivers 3.7 V (do not substitute for 1.5 V AA) Light weight
High power
Available in tool-specific battery packs
*Actual performance will vary with battery maker, model, and condition