9V batteries may not be as top of mind as your phone's battery — until they run out of power. They’re one of the most common sources of power for critical household, health, and work-related electronics, including smoke detectors, personal blood pressure monitors, and job site walkie-talkies.

While all 9V batteries are the same size, and thus completely interchangeable, there can be considerable differences in performance and price. The following article will help you understand what separates them, so you can choose the best 9V batteries for particular functions.

— Best Overall: Energizer Ultimate Lithium 9V Battery — Best Budget: Amazon Basics 9V Performance Battery — Best Rechargeable: LP 9V Rechargeable Battery Charger Pack — Best Alkaline: Duracell CopperTop 9V Battery — Best For Smoke Detectors: PKCell Extra Heavy Duty 9V Battery

Our research involved checking products from all of the leading battery brands so we had a thorough understanding of the various 9V batteries available.

Type: Although there are perhaps a half dozen or more chemical compositions used for 9V batteries, we can narrow it down to three common types: alkaline, lithium, and nickel metal hydride. The first two are generally used for disposable 9V batteries, and the latter for rechargeable 9V batteries (though lithium-ion rechargeables are also available). We have included examples of each in order to provide the widest possible choice.

Performance: Although a 9V battery gives a predetermined amount of power, not all 9V batteries deliver that power with the same consistency, or over the same period. This is a key issue, and specifics are discussed in detail below.

Brand: Cheap 9V batteries are common, but reliability can be a problem, as can leaks that damage equipment. While we didn’t only choose premium brands, we did try to choose those with a proven reputation for quality products.

Why They Made The Cut: Energizer’s Ultimate Lithium 9V battery delivers consistent power for longer than any competitor, has greater shelf life, and can withstand extreme operating temperatures.

— Type: Lithium-Manganese Dioxide — Capacity: 750 milliAmp hours (mAh) — Pack Sizes: One, two, 12, 24

— Market-leading performance — Suitable for all weather conditions — 10-year shelf life

Energizer has been one of the leading developers of advanced lithium battery chemistries that provide better performance for longer, and in more extreme conditions. Their 9V battery uses lithium-manganese dioxide and offers class-leading consistency in terms of power delivery, and provides a shelf life of up to 10 years.

The Energizer Ultimate Lithium 9V battery is certainly expensive. It’s disposable, yet costs more than most rechargeable 9V batteries. On the other hand, the unrivaled durability means it’s the ideal choice for important, high-drain security apparatuses, smart home devices, or personal medical equipment. It is extremely reliable, and the extended run time makes it especially good for equipment that is awkward to reach, thus reducing how often batteries need changing.

These batteries are also the optimum solution for outdoor use. Alkaline versions lose charge rapidly as the temperature drops, but the Energizer Ultimate Lithium 9V battery can function anywhere from minus 40 degrees Fahrenheit to 140 degrees Fahrenheit.

Why They Made The Cut: For many ordinary household gadgets and toys, the money-saving 9V Alkaline batteries from Amazon Basics are a convenient, and perfectly adequate solution.

— Type: Alkaline — Capacity: Not given — Pack Sizes: Four, eight, 24

— Great everyday value — Five year shelf life — Leak-free design

— Not for high-drain devices — Poor in cold weather

For household devices that have modest power demands, lithium 9V batteries are overkill. 9V alkaline disposable batteries, like these Performance Batteries from Amazon Basics, are a reliable, affordable alternative.

These shouldn’t be confused with cheap, bargain-store 9V batteries. Amazon doesn't reveal who makes them (and we were unable to find an mAh rating), but they are a quality product that comes with a solid, leak-free construction and a five-year shelf life.

While not designed for high-drain equipment, Amazon Basics 9V batteries will still run a high-drain gadget for a limited period. So, as well as having them for everyday use, they can be kept as emergency backup in case more powerful alternatives have run flat unexpectedly.

Amazon Basics 9V alkaline batteries have limited cold weather performance, but that’s a drawback with the chemistry, rather than this particular model. While they come in a plain cardboard box that Amazon calls ‘frustration-free’ packaging, each does have a plastic wrap that some find awkward to remove.

Why They Made The Cut: The LP 9V rechargeable pack contains four high-performance lithium-ion batteries, and a smart charger that can individually manage each charge level.

— Type: Lithium-ion — Capacity: 600 mAh — Pack Sizes: One, two, four

— Up to 1,200 recharge cycles — Low self-discharge rate — USB-powered charger

— More expensive than NiMH — Not compatible with all chargers

Although rechargeable 9V batteries are more expensive initially, they can be a very affordable choice over their entire lifetime. That’s especially true of the LP model , which can be recharged up to 1,200 times. Even taking into account the price of the included charger, that works out at a very low unit cost.

It is also a more environmentally friendly approach than disposable batteries. While 9V alkaline batteries are relatively easy to recycle, unfortunately many still find their way into landfill.

The 600 mAh capacity of the LP 9V is also impressive, giving consistent performance for a variety of security and testing devices. They are also one of the best for guitar use and other sound equipment. These are low self-drain batteries, retaining up to 75 percent of charge over a threeyear period.

The charger itself can be powered by any device with a micro USB port and has a microchip that allows it to control each charging port individually. We recommend this option, because the LP batteries might fail to charge fully on some other chargers.

Why They Made The Cut: Duracell claims to be the world’s most trusted battery brand, and has a long-standing reputation for reliable performance at reasonable cost.

— Type: Alkaline — Capacity: 310 mAh — Pack Sizes: One, two, four, eight, 12

— Dependable performance — Leak-proof construction — Fiveyear shelf life

— Not for high-drain devices — Not rechargeable

The big challenge with some cheap disposable 9V batteries is the inconsistency of their performance. One might be fine, the next one out of the pack seems to have run flat almost as soon as it is installed. Duracell CopperTop 9V batteries are intended to overcome this problem by providing dependable power without the expense of lithium models.

The 9V Duracell CopperTop batteries are not intended to compete with high-performance alternatives, and although they will power high-drain gadgets, that’s not their primary purpose. These batteries are targeted at those who want reliability from their everyday electronic devices. The 310 mAh isn’t spectacular, but it is better than many alkaline rivals. This gives it the consistency the brand is renowned for, and as a result, it is tremendously popular.

Unlike cheap 9V alkaline batteries, the Duracell CopperTop batteries  don’t leak during normal use. They contain no harmful chemicals, so they are relatively easy to recycle. As with all alkaline batteries, performance does drop significantly in cold weather, so we would not recommend the Duracell CopperTops for outdoor use in winter.

Why They Made The Cut: PKCell 9V batteries use unusual carbon zinc chemistry that produces modest power output, but only for extended time periods.

— Type: Carbon Zinc — Capacity: 400 - 500 mAh (see below) — Pack Sizes: Two, 10, 24, 100

— Long-lasting power — Threeyear shelf life — Very competitive price

— Modest performance — Inconsistent quality control

The PKCell 9V batteries are unusual in that they use carbon zinc chemistry. This is seldom found because, although costs are low, energy delivery is poor, even when compared to budget alkaline batteries. However, carbon zinc 9V batteries have a relatively high capacity so they can hold their power for longer. They also work better in the cold than alkaline batteries.

This makes them an excellent choice for low-drain devices like smoke detectors, fire alarms, and other monitoring equipment that demands modest battery performance, but over as long of a time period as possible. While PKCell themselves don’t provide capacity figures, independent reviewers have rated them at between 400 and 500 mAh. That’s much better consistency than alkaline 9V batteries, and as good as some lithium models.

It is important to understand the focus of the PKCell 9V battery. It may be called ‘Extra Heavy Duty’ on the packaging, but it isn’t. It will not run power-intensive devices. What it will do is provide low power, for a long time, at very little cost.

The key difference between types of 9V battery is the chemistry used to store the electrical charge.

Alkaline 9V batteries are the budget option. The provide proven, reliable technology best suited to low-performance devices (often called low-drain) like radios, clocks, or hand-held remote controls. Alkaline 9V batteries are not rechargeable.

There are a number of variations on lithium battery chemistry, and it is an area of ongoing development. 9V batteries are often simply called lithium (Li), or may be lithium-manganese dioxide (LiMnO2). Lithium 9V batteries are recommended for high-drain devices like medical or testing equipment where reliability and stability are of prime importance. Lithium 9V batteries are more expensive than alkaline and many types are not rechargeable. The exception is lithium-ion (Li-ion) 9V batteries, which are rechargeable.

9V NiMH batteries are a popular rechargeable option. In both performance and price terms, they usually sit somewhere between alkaline and lithium. The fact that they can be recharged hundreds of times means they are economical in the long run. The drawback with NIMH 9V batteries is that they lose charge over time and new batteries may need to be charged before use. Some are low self-drain (LSD), meaning this problem is much less pronounced.

Even when two 9V batteries share the same chemistry, there can be differences in how long they can supply their power. The figure used is milliAmp hours (mAh), and it’s often compared to the amount of fuel in a car’s gas tank. For example, if one 9V battery is rated for 400 mAH, and another for 600 mAH then the latter will continue to deliver its charge when the former has run flat. Maximizing 9V battery mAh is important for devices that need to run unattended for long periods.

9V batteries are used in a variety of small electronic devices including smoke and carbon monoxide alarms, circuit testers, blood pressure monitors, walkie-talkies, portable radios, and more.

In most devices, a significant drop in performance or failure to operate will indicate you should replace your 9V battery. Alarms usually have a recommended replacement of six or 12 months.

Much depends on the equipment being powered, but typically AA batteries have a higher milliAmp hour (mAh) rating, so tend to last longer than 9V models.

Much depends on the battery, and the charger. Our research shows charging times vary considerably from a low of around three hours to eight hours or more.

While it’s possible they may last more than a year, most smoke alarm manufacturers recommend that they are replaced every six months.

Advice varies. While some say 9V batteries should be considered dead at 8V or below, numerous devices (typically meters and measuring equipment) will still function at 7V or even 6.5V.

Energizer’s 9V Ultimate Lithium batteries are head-and-shoulders above the competition in performance terms. They store longer, run longer, and function at greater temperature extremes. They are undeniably expensive, but if you want a battery you can rely on in harsh conditions these are the ones to choose. At the other end of the price scale are the Amazon Basics All-Purpose Alkaline , cheap 9V batteries that are more than adequate for dozens of everyday gadgets.

This post was created by a non-news editorial team at Recurrent Media, Futurism’s owner. Futurism may receive a portion of sales on products linked within this post.