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Lithium Lawn Mower Battery Guide: Group U1, 390 CCA, 2.76 lb
Short answer: A lithium lawn mower battery like the Pro-Guide U1X is a 12.8V LiFePO4 starting battery in the Group U1 size (6.85 x 4.84 x 6.42 in) that delivers 390 CCA (lead-acid equivalent) and weighs just 2.76 lb. It is built for riding mowers, garden tractors and other small engines that take a U1 battery, holds its charge through the off-season with less than 3% self-discharge per month, and is backed by a 3-year free replacement warranty.
Few things are more frustrating than the first warm Saturday of spring, a full gas tank and a mower that just clicks. Lead-acid U1 batteries lose charge sitting in a cold garage all winter, and many owners end up buying a new one every few seasons. This guide explains what a Group U1 battery is, what 390 CCA means for your mower, how a lithium U1 compares with lead-acid, how to charge and store the U1X, and how it differs from our larger marine starting battery.
Key Takeaways
- Starting power: 390 CCA lead-acid equivalent (PbEq), with Pro-Boost technology for added starting power.
- Featherweight: 2.76 lb (1.25 kg), easy to lift in and out of a mower.
- Ready after winter: less than 3% self-discharge per month.
- Standard U1 size: 6.85 x 4.84 x 6.42 in with two M6 threaded terminals.
- Built-in gauge: a battery capacity indicator shows FUL, MED or LOW at the press of a button.
- Durable: more than 1,000 cycles at 100% depth of discharge, IP65 rated, 3-year free replacement warranty.
What Is a Group U1 Battery?
"U1" is a Battery Council International (BCI) group size used mainly for lawn and garden equipment: riding mowers, lawn tractors, garden tractors and some zero-turn mowers, plus other small-engine machines. Like every BCI group number, it describes the case dimensions and layout, not the chemistry inside.
Most U1 batteries are flooded or sealed lead-acid. They work, but they are heavy for their size, they self-discharge over the off-season, and a deeply drained lead-acid battery often never fully recovers. A Group U1 lithium battery keeps the same size but swaps the lead plates for lithium iron phosphate (LiFePO4) cells, which hold their voltage under load, weigh much less and lose far less charge in storage.
The Pro-Guide U1X (PGLU1X) is our 12.8V LiFePO4 starting battery in that U1 size, rated at 390 CCA lead-acid equivalent.
Pro-Guide U1X Specifications
| Model / SKU | Pro-Guide U1X (PGLU1X) |
| Battery type | Lithium starting battery (LiFePO4) |
| Cranking | 390 CCA lead-acid equivalent (PbEq), Pro-Boost |
| Nominal voltage | 12.8V |
| Capacity / energy | 3Ah / 36Wh |
| Cycle life | 1,000+ cycles at 100% DoD |
| Charge current | 1.5A standard, 15A maximum continuous |
| Discharge cut-off | 8V |
| Self-discharge | Less than 3% per month |
| Charging temperature | -4°F to 113°F (-20°C to 45°C) |
| Discharge temperature | -4°F to 140°F (-20°C to 60°C) |
| Storage temperature | -4°F to 104°F (-20°C to 40°C) |
| Protection | IP65 |
| Features | Built-in state of charge gauge, Pro-Boost |
| Terminals | 2 x M6 internal thread |
| Dimensions | 6.85 x 4.84 x 6.42 in (174 x 123 x 163 mm) |
| Weight | 2.76 lb (1.25 kg) |
| Warranty | 3-year (36-month) free replacement |
Download the U1X data sheet (PDF).
The Pro-Guide U1X in its Group U1 case, shown with its two threaded terminals. At 2.76 lb, it lifts in and out with one hand.
Is 390 CCA Enough to Start a Riding Mower?
Cold cranking amps (CCA) describe how much current a battery can deliver to a starter in cold conditions. The U1X is rated at 390 CCA expressed as a lead-acid equivalent (PbEq), so you can compare it directly with the CCA printed on a conventional U1 battery. Pro-Boost technology adds starting power on top of that.
To confirm the fit for your machine, check your owner's manual or the label on your current battery for its minimum CCA requirement, then make sure the U1X meets or exceeds it. Most owners only need to answer two questions:
- Does my equipment take a Group U1 battery? Compare your tray with the U1X's 6.85 x 4.84 x 6.42 in size and check terminal clearance.
- Does 390 CCA meet the manufacturer's requirement? If your current battery is rated at or below 390 CCA, the U1X meets it.
One thing the U1X is not: an accessory battery. With 3Ah (36Wh) of capacity, it is built to start engines, not to run lights, sprayers or electronics for long periods with the engine off. Your mower's charging system takes over once the engine is running.
Lithium also helps with consistency. A LiFePO4 battery holds its voltage under load, so it cranks at a steady voltage rather than slowing as it drains, which is where tired lead-acid mower batteries often fail.
Lithium vs. Lead-Acid Lawn Mower Batteries
| Factor | Pro-Guide U1X (LiFePO4) | Typical lead-acid U1 battery |
| Weight | 2.76 lb | Several times heavier |
| Self-discharge in storage | Less than 3% per month | Typically higher; often needs a maintainer over winter |
| Voltage while cranking | Steady until nearly empty | Drops as the battery drains |
| Cycle life | 1,000+ at 100% DoD | Shorter, especially after deep discharges |
| Maintenance | None; no water, no acid | Flooded types need water checks and terminal cleaning |
| State of charge | Built-in FUL / MED / LOW gauge | Usually needs a voltmeter |
| Warranty | 3-year free replacement | Often shorter |
The self-discharge number is the one that matters most for seasonal equipment. At less than 3% per month, a fully charged U1X that sits for a four-month winter should still have most of its charge in spring. A lead-acid battery left in the same garage often needs a charger or maintainer to avoid starting the season flat, and a lead-acid battery that sits discharged for long periods can be permanently damaged.
What Is the U1X Best For?
- Riding mowers and lawn tractors that take a Group U1 battery.
- Garden tractors and zero-turn mowers with a U1-size tray (confirm dimensions and CCA first).
- Other small-engine equipment that uses a U1 starting battery.
- Seasonal and occasional-use machines that sit for weeks or months, where low self-discharge matters most.
- Anyone tired of lifting heavy batteries: at 2.76 lb, swapping or removing the battery for storage is easy.
Matched add-ons include the NOCO Group U1 Snap-Top Battery Box for a secure, covered installation, and the 12V 500A Jump Starter to keep in the garage for any engine that needs a boost.
The top of the U1X shows its two terminals, the charging cautions and sleep and wake-up steps, and the built-in FUL / MED / LOW battery capacity indicator.
How to Charge a Lithium U1 Battery
During normal use, your mower's charging system recharges the U1X while the engine runs. For off-season top-ups or after a hard start, use a battery charger. Charge time is roughly capacity divided by charger output:
- 1.5A standard charge: about 2 hours from empty.
- 15A maximum continuous: about 12 minutes from empty. Do not use a charger that delivers more than 15A.
Charging rules from the battery label:
- Use a charger with a LiFePO4 (lithium) charging profile. Both the vehicle and the battery charger should limit voltage to 14.0V to 15.0V when charging, and the label says not to charge the battery above 15.0V.
- Don't use a charger with an automatic "desulfation" function. That mode is designed for lead-acid batteries.
- If the battery becomes hot to the touch, stop charging and let it cool before resuming.
- Know your voltages: the label lists 13.4V as 100% charged and 13.05V as 30% charged.
- Charge within -4°F to 113°F (-20°C to 45°C).
Shop lithium-compatible options in our battery chargers collection.
Install, Storage and Off-Season Tips
Wake it up before the first start
Hold the TEST button for 1 second: the green lights illuminate from bottom to top, then the middle green light turns off after 5 seconds.
Check state of charge
In wake-up mode, quickly press TEST. The battery capacity indicator shows FUL, MED or LOW. If it reads LOW, recharge immediately.
Put it to sleep for storage
The label recommends disconnecting the battery cables when the equipment is used infrequently or stored, and manually putting the battery into sleep mode: hold TEST for 3 seconds until the middle red light illuminates; the red light turns off when you release the button. Store it between -4°F and 104°F (-20°C to 40°C).
Keep it dry and secure
The U1X is IP65 rated: dust-tight and protected against water jets, such as hosing off the deck. It is not rated for immersion, so keep it in its tray away from standing water. Keep the terminals clean and securely fastened, and never attempt to open the battery.
U1X vs. 24M100-ST: Small Engine or Marine Starting?
Both are Pro-Guide LiFePO4 starting batteries, but they are built for very different engines.
| Spec | U1X | 24M100-ST |
| Built for | Lawn and garden, small engines | Marine outboard starting |
| Cranking | 390 CCA (PbEq) | 1,000 CCA (PbEq) |
| Capacity | 3Ah / 36Wh | 100Ah / 1,280Wh |
| Group size | U1 | 24 |
| Weight | 2.76 lb | 28.7 lb |
| Warranty | 3-year free replacement | 3-year free replacement, 10-year pro-rata |
Choose the U1X for your mower or small engine. If you also have a boat, the 24M100-ST is the lithium starting battery for your outboard, with enough capacity to run electronics too. Browse all lithium starting batteries to compare.
Frequently Asked Questions
Can I put a lithium battery in my lawn mower?
Yes, if it matches your mower's group size and cranking requirement. The Pro-Guide U1X is a Group U1 LiFePO4 starting battery rated at 390 CCA lead-acid equivalent.
How many cold cranking amps does the Pro-Guide U1X have?
The U1X is rated at 390 CCA lead-acid equivalent (PbEq), and its Pro-Boost technology adds starting power.
Will the U1X fit my equipment's Group U1 battery tray?
The U1X measures 6.85 x 4.84 x 6.42 in, a Group U1 size. Measure your tray and check terminal clearance before installing.
How much does the U1X weigh?
2.76 lb (1.25 kg), much lighter than a lead-acid battery of the same group size.
Will the U1X hold a charge over the winter?
It is rated at less than 3% self-discharge per month. Disconnect the cables and put it into sleep mode for storage, and keep it between -4°F and 104°F.
How long does it take to charge the U1X?
About 2 hours from empty at the standard 1.5A, or about 12 minutes at the 15A maximum. Use a LiFePO4 charging profile and never exceed 15.0V.
Is the U1X waterproof?
It is IP65 rated: dust-tight and protected against water jets. It is not rated for immersion.
What warranty comes with the U1X?
A 36-month (3-year) free replacement warranty.
Make This the Last Mower Battery You Buy for a While
If your mower or garden tractor takes a Group U1 battery, the Pro-Guide U1X gives you 390 CCA of steady starting power in a 2.76 lb package that holds its charge through the off-season. No acid, no watering, a built-in charge gauge and a 3-year free replacement warranty.
Not sure the U1X fits your equipment? Call our team at 1-800-827-3232 or browse all lithium starting batteries and lithium batteries.
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