Top 4 Greenworks 40V 4.0Ah Battery Options for 2026

Your string trimmer sputters halfway down the fence line. The mower dies with one strip of grass left near the curb. That dead 40V battery in your garage isn’t just an inconvenience—it’s the reason your yard looks half-finished.

Replacing it shouldn’t require a degree in electrical engineering, but the choices are confusing. Genuine Greenworks packs cost more. Third-party replacements promise double the runtime for less money. Sorting out which one actually works with your specific tool takes patience most of us don’t have.

I’ve broken down the four most common 40V 4.0Ah options you’ll find on Amazon right now. These range from the official OEM battery to high-capacity aftermarket alternatives. My goal is simple: help you pick the one that fits your tools, your budget, and your tolerance for risk.

Here is a quick look at how these four contenders stack up on paper.

Features	Genuine 4.0Ah (New)	Genuine 4.0Ah (Standard)	Amityke 2-Pack	Forrat 6.0Ah
Battery Type	Genuine OEM	Genuine OEM	Aftermarket	Aftermarket
Capacity	4.0Ah	4.0Ah	4.0Ah each	6.0Ah
Key Feature	22% Power Boost	Standard Power	Best Value	Longest Runtime
Compatibility	75+ Tools (Gen 2)	75+ Tools	Gen 2 Tools Only	Gen 2 Tools Only
Warranty	Official	Official	12 Months	Not Specified

Greenworks High-Power Battery

This is the newest iteration of the genuine 40V 4.0Ah pack, and it brings a noticeable performance edge. Greenworks states this version delivers a 22% power boost over previous generations. For anyone using a high-draw tool like a leaf blower or a chainsaw, that extra push translates to better performance when the load gets heavy.

The integrated LED fuel gauge sits right on the pack, so you can check remaining charge without plugging it into a tool. It works with the same 75+ tool ecosystem as older packs, making it a drop-in upgrade for most modern Greenworks equipment. The internal battery management system handles over-voltage, over-current, and short-circuit protection so the cells stay healthy through many charge cycles.

Here’s the honest catch: this battery only fits second-generation 40V tools. If you own an older first-generation G-MAX device, this pack won’t slide in. Also, the power boost only matters if your tool can actually draw that extra current—a basic string trimmer might not feel much different, though runtime remains solid.

• Official Greenworks product with full manufacturer warranty
• 22% power boost for demanding tools
• Built-in LED charge indicator
• Multi-protection BMS for overheat and short-circuit safety
• Compatible with 75+ Greenworks tools

Best for: Owners of modern Gen 2 Greenworks tools who want genuine OEM reliability with a little extra muscle for blowers and chainsaws.

Greenworks Standard Battery

This is the workhorse pack that has powered Greenworks yards for years. It’s a genuine OEM battery without the recent power-boost update, but it carries the same trusted build quality and safety circuitry. If you’re replacing a worn-out pack for a mower or trimmer and just want things to work, this is the safest bet.

Because it’s a genuine Greenworks product, you get the official warranty and the assurance that the battery management system matches what your tool expects. Aftermarket packs sometimes cause tools to run in a degraded mode or shut off unexpectedly; this one communicates properly with the equipment. The 4.0Ah capacity offers a balanced runtime for most residential tasks—enough to finish a typical driveway edging session or a small lawn mow.

The trade-off is straightforward: you pay more for the name and the safety net. This pack doesn’t offer the extended runtime of a 6.0Ah aftermarket unit, and it lacks the 22% boost of the newer version above. For basic tools, you won’t notice the difference, but the price gap between this and third-party options can be significant.

• Genuine Greenworks battery with official warranty
• Compatible with 75+ tools in the 40V lineup
• No memory effect after repeated charging
• Fade-free power delivery until the cell is depleted
• Proven reliability over many charge cycles

Best for: Users who prioritize warranty protection and guaranteed compatibility over saving a few dollars on a knockoff pack.

Amityke 2-Pack Battery

Running multiple 40V tools usually means you need more than one battery. The Amityke 2-pack solves that problem at a price point that undercuts buying two genuine OEM units. Each battery delivers 4.0Ah of capacity, giving you a spare ready to go when the first pack drains.

These packs are built to replace Greenworks 29472 and 29462 models, fitting a wide range of second-generation tools. The included dual-port charger is a practical bonus—you can top off both batteries simultaneously, which cuts downtime significantly during big yard projects. Each pack has a four-LED indicator so you can see remaining charge at a glance.

Before you buy, check your tool’s generation carefully. This battery is strictly for Gen 2 equipment; it will not work with older first-generation G-MAX tools. The build quality won’t match OEM standards—the plastic casing feels slightly less robust, and the cells inside are not Greenworks-sourced. Amityke provides a 12-month support window, but that’s shorter than the official warranty on genuine packs.

• Two 4.0Ah batteries plus a dual-port charger included
• Compatible with Gen 2 Greenworks tools only
• Four LED indicators on each battery
• Built-in protection against overcharge and short-circuit
• High-capacity 4000mAh cells for extended runtime

Best for: Homeowners with multiple Gen 2 Greenworks tools who need a spare battery and charger without paying OEM prices.

Forrat 6.0Ah Replacement

Sometimes 4.0Ah just isn’t enough. The Forrat replacement bumps capacity to 6.0Ah, offering roughly double the runtime of a standard 3.0Ah pack. For larger yards or heavy tasks like mowing thick grass, this extended capacity means fewer interruptions to swap batteries.

The higher watt-hour rating (240Wh) delivers consistent power for demanding tools like lawn mowers and snow blowers. It maintains the same footprint as the standard 4.0Ah pack, so it fits existing tools without any modification. The four LED indicators give you a clear picture of remaining charge, helping you plan when to head back to the charger.

The main concern with any high-capacity aftermarket battery is heat. Drawing more current from a larger pack can generate more heat during sustained use, and the Forrat pack doesn’t have the advanced thermal management of the genuine Greenworks units. It also only fits Gen 2 tools, so verify your equipment before ordering. The warranty situation is less clear than with OEM products, which adds a small element of risk.

• 6.0Ah capacity for extended runtime
• 240Wh power output for high-draw tools
• Fits Gen 2 Greenworks 40V tools
• Four LED charge indicators
• Protection against overcharge, over-discharge, and short-circuit

Best for: Users with high-drain tools like mowers who want maximum runtime per charge and don’t mind aftermarket build quality.

How We Chose These Products

I started by looking at what actually sells and what real users complain about in reviews. The Greenworks 40V platform has a massive install base, so battery failures and compatibility issues generate a lot of discussion. I focused on packs that consistently work across multiple tool types rather than those with frequent DOA reports.

My evaluation weighed three factors: genuine OEM reliability versus aftermarket savings, capacity relative to real-world runtime needs, and generation compatibility confusion. I excluded any battery that had widespread reports of fitting issues or tool damage. The four options here represent the sweet spot of what most homeowners actually consider when searching for a replacement.

Buying Guide: What Really Matters

The first thing to determine is which generation of Greenworks tools you own. First-generation G-MAX tools use a different battery interface than the second-generation models. Most current listings specify Gen 2 compatibility, but if you have older equipment, you need to check the model number carefully. Buying the wrong generation means the battery simply won’t click into place.

Capacity directly affects runtime, but bigger isn’t always better. A 6.0Ah battery weighs more and costs more than a 4.0Ah unit. For a lightweight hedge trimmer, the extra capacity adds unnecessary weight that fatigues your arms. For a mower or blower, the extended runtime is worth the heft. Match the capacity to the tool’s draw and the size of your yard.

Genuine batteries cost more for a reason: they include safety circuits that prevent over-discharge and thermal runaway, plus they carry the official warranty. Aftermarket packs save money but often skimp on cell quality and protective electronics. If you store batteries in a hot garage or use them heavily, OEM packs offer more peace of mind. If budget is tight and your tools are out of warranty anyway, a reputable third-party option can work fine.

Our Top Recommendation

The Greenworks 40V 4.0Ah High-Power Battery is the clear winner. It delivers genuine OEM quality, the 22% power boost actually helps with blowers and chainsaws, and the LED indicator is genuinely useful. You pay more upfront, but you avoid the risk of a third-party pack damaging your tool or dying after a few months.

If you’re on a tight budget and own multiple tools, the Amityke 2-Pack offers the best value—just verify your tools are Gen 2 before purchasing. For those who need maximum runtime for a mower, the Forrat 6.0Ah is worth considering, but accept the aftermarket trade-offs. The standard Greenworks battery remains a solid choice if you find a good price and don’t need the power boost.

Frequently Asked Questions

How do I know if my tool is Gen 1 or Gen 2?
Check the model number on the tool itself. Gen 2 tools typically have model numbers starting with 25 or higher (like 25312 or 29252). Gen 1 G-MAX tools usually have model numbers in the 22xxx range or earlier. When in doubt, look up your specific model on the Greenworks website before ordering a replacement battery.

Can I use a 6.0Ah aftermarket battery with my original Greenworks charger?
Yes, in most cases. The charger communicates with the battery’s management system to regulate charging. However, aftermarket batteries sometimes have slightly different charging profiles. If the battery gets hot during charging or the charger shows an error light, stop using it immediately and switch back to a genuine pack.

Why does my new battery die faster than my old one?
Lithium-ion batteries degrade over time, but a new battery should perform better than an old one. If it doesn’t, you might have received a counterfeit or a pack with lower-quality cells. Also, cold weather temporarily reduces battery capacity. Store your batteries indoors during winter months to maintain peak performance.

Is it safe to leave my battery on the charger all winter?
No. Leaving a lithium-ion battery at full charge for extended periods stresses the cells and shortens lifespan. Store batteries at about 50% charge in a cool, dry place if you won’t use them for several months. Check the charge level every couple of months and top it up to 50% if it drops below 30%.