Best 9V Lithium Batteries for Alarms: 2025 Expert Review
Oli at OR Electrics
18th Edition Qualified Electrician
Nothing is more annoying than a smoke alarm chirping 'low battery' at 3am. But beyond the nuisance, it is a serious safety issue. In my line of work across Leeds, I frequently encounter alarms that have failed simply because the battery couldn't handle a cold snap or just ran out of juice too quickly.
Many homeowners rely on standard alkaline batteries, but lithium is often the superior choice for smoke and fire alarms. They handle temperature fluctuations better—crucial in our drafty Victorian housing stock—and generally last much longer, meaning you aren't dragging the ladder out every six months.
In this review, I'm comparing three lithium options: a budget-friendly rechargeable unit, the 'gold standard' install-and-forget primary cell, and a high-capacity problem solver. I'll explain which ones are safe for your specific setup.
Live in Leeds?
Unsure if your alarms are compliant?
Get a safety check from our local team.
Specs vs. The Real World
The Spec: "10-Year Battery Life"
"Manufacturers claim the battery lasts 10 years, matching the lifespan of the alarm itself."
This assumes 'standby' mode. If you have frequent false alarms (burnt toast) or test it weekly, that lifespan drops. However, lithium will still massively outperform alkaline.
The Spec: "Rechargeable Voltage"
"You can swap any 9V battery for a rechargeable one to save money."
Be careful. Standard 9V is actually around 9.6V when fresh. Some rechargeable lithiums output a strict 9V or dip suddenly. Always check your alarm's manual to ensure it supports rechargeable cells.
My Top 3 Recommendations
Three options to cover different needs and budgets
Delyeepow 9V Rechargeable Battery USB Rechargeable (1-Pack)
Delyeepow
If you are looking for a low-cost entry into lithium power, this Delyeepow unit is a decent starting point. It's incredibly convenient thanks to the USB-C charging port directly on the battery, removing the need for a bulky classic charger.
The Good
- Very affordable price point
- Direct USB-C charging is convenient
- No memory effect unlike older NiMH batteries
The Bad
- 650mAh capacity is on the lower side
- Single pack only
Installer Tip:
This is great for accessible devices, but with 650mAh, I wouldn't put it in a high-ceiling alarm you can't reach easily. Stick to using this in your multimeter or accessible tabletop devices.
Priced at £6.99 at the time of writing
Check Price on AmazonEnergizer Ultimate Lithium 9V Batteries (2 Pack)
Energizer
This is the gold standard. When I'm fitting alarms in a rental property in Headingley, this is what I recommend. These are single-use (primary) lithium batteries, meaning they hold charge for up to 10 years and don't leak. They work perfectly in the cold, making them ideal for garages or attics.
The Good
- The longest-lasting option for smoke alarms
- Leak-resistant construction protects your device
- Performs in freezing temperatures (great for garages)
The Bad
- Higher upfront cost
- Not rechargeable
Installer Tip:
Use these for 'hard-wired' alarms with battery backup. Since the battery is only used during power cuts, these Ultimate Lithiums often last the entire 10-year life of the alarm without ever needing changing.
Priced at £22.93 at the time of writing
Check Price on AmazonENEGON 9V Rechargeable Battery, 12150mWh High Capacity (2-Pack)
ENEGON
If you have a device that eats batteries for breakfast—like a high-sensitivity carbon monoxide detector or wireless security sensor—these ENEGONs are the solution. With double the capacity of standard budget rechargeables (1350mAh), they bridge the gap between convenience and longevity.
The Good
- Massive 1350mAh capacity lasts longer between charges
- Fast USB-C charging (1.5 hours)
- Built-in safety protection against overheating
The Bad
- Dimensions can sometimes be a tight fit in older battery compartments
- Requires discipline to recharge
Installer Tip:
Always fully charge these and cycle them a few times when you first get them to get maximum capacity. If using in an alarm, ensure you have a schedule to check the level, as lithiums don't 'fade' like alkalines—they cut off sharply.
Priced at £14.99 at the time of writing
Check Price on AmazonFrequently Asked Questions
Can I put lithium batteries in any smoke alarm?
Why do my smoke alarms chirp at night?
Are rechargeable batteries safe for smoke alarms?
How often should I change lithium alarm batteries?
Do you install mains-powered alarms in Leeds?
Need Professional Smoke & Fire Alarm Systems?
Our team at OR Electrics specialises in Smoke & Fire Alarm Systems across Leeds.
Get a free quote for professional installation.
View Our Smoke & Fire Alarm Systems Service