Replacement Batteries for Your Generac Generator
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Generac is one of the best-known names in home and portable generators, and many of its portable models use a small 12-volt battery to power the electric start button. When that battery wears out, the generator still has a pull cord, but the push-button start stops working. The batteries in this guide are not made by Generac. They are third-party replacement batteries built to match the size and voltage of the originals, and each listing names the Generac models it is meant to fit. Knowing that up front helps you shop with the right expectations.
In one sentence: four listings are the same 12V 9Ah Mighty Max battery labeled for different Generac models, one is a larger 12V 18Ah Mighty Max battery for the 7500 EXL, and one is a Casil 12V 9Ah battery matched by Generac part number.
Generac Replacement Batteries Compared
| Model | Voltage and capacity | Named Generac fit | Size (inches) | Pack |
|---|---|---|---|---|
| Mighty Max Battery 12V 9AH Battery (XG8000E) | 12V 9Ah | XG8000E | 5.94 x 2.56 x 3.94 | 1 |
| Mighty Max Battery 12V 18AH SLA | 12V 18Ah | 7500 EXL | 7.12 x 3.00 x 6.50 | 1 |
| Mighty Max Battery 12V 9AH SLA (GP7500) | 12V 9Ah | GP7500 | 5.94 x 2.56 x 3.94 | 1 |
| Mighty Max Battery 12V 9AH Battery (XG8000) | 12V 9Ah | XG8000 | 5.94 x 2.56 x 3.94 | 1 |
| Mighty Max Battery 12V 9AH SLA 4 Pack | 12V 9Ah | XP10000E | 5.94 x 2.56 x 3.94 | 4 |
| Casil 12V 9Ah Generator Battery | 12V 9Ah | GP7500E, XP8000E, XG8000E | Not listed | 1 |
Some quick terms. 12V is the voltage, and it must match your generator. Ah, or amp-hours, is capacity: how much energy the battery holds. SLA means sealed lead acid, and AGM (absorbed glass mat) is a type of SLA where the liquid is soaked into glass fiber mats, which makes it spill proof and maintenance free. You never add water to these batteries.
Mighty Max Battery 12V 9AH Battery for the Generac XG8000E
Mighty Max Battery
Mighty Max Battery 12V 9AH SLA Replacement Battery for XP10000E Generac Electric Portable Generator – 4 Pack
Price and specifications are read from the Amazon product page and can change.
Mighty Max Battery 12V 9AH SLA
Best for: Keeping spares for several generators
Pros
- Four 9Ah batteries in one pack
- UL certified
- One year warranty
Cons
- More than most homes need
- Sealed batteries slowly self-discharge in storage
Best for: XG8000 owners needing a starter battery
Pros
- 12V 9Ah sealed lead acid
- Resists shock and vibration
- One year warranty
Cons
- Battery only, no mounts
- Third-party, not Generac made
Best for: GP7500 owners replacing a dead battery
Pros
- 12V 9Ah sealed lead acid
- Spill proof AGM
- Nut and bolt terminals
Cons
- Battery only, no harness
- Third-party, not Generac made
Best for: Generac 7500 EXL owners
Pros
- 18Ah, double the 9Ah capacity
- Deep discharge recovery
- Screws included
- UL certified
Cons
- Larger 7.12 x 3 x 6.5 inch size
- 9 pounds
Best for: XG8000E owners needing a starter battery
Pros
- 12V 9Ah sealed lead acid
- UL certified
- Mounts in any position
- One year warranty
Cons
- Battery only, no harness
- Third-party, not Generac made
The Mighty Max Battery 12V 9AH Battery is labeled as a replacement for the Generac XG8000E portable generator. Its model is the ML9-12NB, a 12-volt, 9 amp-hour sealed lead acid battery that is UL certified, meaning it has been checked against a recognized safety standard. It measures 5.94 by 2.56 by 3.94 inches and weighs 5.3 pounds, with nut-and-bolt terminals, the type where a small bolt clamps your generator’s wires to the battery.
The listing describes it as an SLA/AGM spill-proof battery with a high discharge rate, wide operating temperatures and long service life. It can be mounted in any position, resists shock and vibration, and comes with a full one-year warranty. The listing is clear that you get the battery only, with no wire harness or mounting accessories, so you reuse the cables and bracket from your old battery.
This is the listing to choose if you own an XG8000E and searched for a Generac XG8000E battery. If you own a GP7500 or XG8000, the same battery appears in its own listings below, so pick whichever listing names your model to make returns simpler.
Mighty Max Battery 12V 18AH SLA for the Generac 7500 EXL
The Mighty Max Battery 12V 18AH SLA is the ML18-12, and it is the only larger battery in this group. It is still 12 volts, but its capacity is 18 amp-hours, double the 9Ah models, and it is physically bigger at 7.12 by 3.00 by 6.50 inches and 11.9 pounds. The listing names the Generac 7500 EXL portable generator as its match.
Like the smaller batteries, it is UL certified, sealed, spill proof, maintenance free and mountable in any position. This listing adds “deep discharge recover,” meaning it is described as recovering well after being drained low. Screws are included, but no wire harness or mounting accessories. It carries a one-year warranty.
If you searched for a Generac 7500 EXL battery, this is the listing that names it. Because the size is quite different from the 9Ah batteries, do not buy it for a model that uses the smaller battery; it will not fit the same tray.
Mighty Max Battery 12V 9AH SLA for the Generac GP7500
The Mighty Max Battery 12V 9AH SLA listing is labeled for the Generac GP7500 portable generator. It is the same ML9-12NB battery as the XG8000E listing: 12 volts, 9 amp-hours, 5.94 by 2.56 by 3.94 inches, nut-and-bolt terminals, UL certified and covered by a one-year warranty.
It is spill proof and maintenance free, handles high and low temperatures, and resists vibration, which matters on a generator that shakes while it runs. Again, the battery comes alone, without harness or mounts. The listing does not state a weight, but the matching listings give 5.2 to 5.3 pounds for the same model.
Anyone looking for a Generac GP7500 battery can start here. To learn more about the generator lineup itself, our Generac home generator guide explains the difference between portable and standby units.
Mighty Max Battery 12V 9AH Battery for the Generac XG8000
This second Mighty Max Battery 12V 9AH Battery listing names the Generac XG8000 rather than the XG8000E. The battery is once more the ML9-12NB, 12 volts and 9 amp-hours, with the same dimensions, nut-and-bolt terminals, UL certification and one-year warranty. The listed weight is 5.2 pounds.
It is sealed, spill proof, maintenance free, and can be mounted in any position. Battery only, no wire harness or mounts. Choose this listing if your generator’s label reads XG8000.
Mighty Max Battery 12V 9AH SLA 4 Pack for Multiple Generators
The Mighty Max Battery 12V 9AH SLA four-pack contains four ML9-12NB batteries and is labeled for the Generac XP10000E electric-start portable generator. Each battery matches the others in this guide: 12 volts, 9 amp-hours, 5.94 by 2.56 by 3.94 inches, nut-and-bolt terminals, UL certified, with a one-year manufacturer’s warranty.
A four-pack makes sense for someone who looks after several generators, such as a small contractor or a family with generators at more than one property. For a single home generator, one battery is enough. As a general rule, sealed lead acid batteries slowly lose charge on the shelf, so spares should be topped up from time to time.
Casil 12V 9Ah Generator Battery for Part Number Matching
Casil
Casil 12V 9Ah Generator Battery – SLA AGM Replacement for Generac GP7500E, XP8000E, XG8000E, 0G9449, HSL1069, 6-FM-9A, HW-9-12
Price and specifications are read from the Amazon product page and can change.
Casil 12V 9Ah Generator Battery
Best for: Matching by part number 0G9449
Pros
- 12V 9Ah SLA AGM
- Lists many Generac models
- Cross-references HSL1069, 6-FM-9A
Cons
- Prorated warranty
- Dimensions not listed
The Casil 12V 9Ah Generator Battery is a third-party SLA AGM battery from a different maker. Its listing is built around part numbers: it names Generac’s 12V sealed battery part 0G9449 and cross-references HSL1069, 6-FM-9A and HW-9-12. It names the GP7500E, XP8000E and XG8000E generators.
It is 12 volts and 9 amp-hours, rechargeable, with a one-year prorated warranty, meaning the coverage value decreases over the year. The listing does not specify dimensions, terminal type or weight, so compare it to your old battery before ordering. It suits someone who has the part number from their old battery or manual and wants to match it directly.
How to Choose the Right Battery for Your Generac Generator
Start with your generator’s model number, printed on a label on the frame. Then find the listing that names it. That is the simplest way to answer the question of which battery fits your Generac.
Next, match voltage and capacity. All six are 12 volts. Five are 9Ah and share one size; the 18Ah battery is larger and suited to the 7500 EXL. Buying a bigger battery for a small tray will not work.
Then check terminals and size. The Mighty Max listings give nut-and-bolt terminals and exact dimensions, while the Casil listing does not list either. Measure your old battery if unsure. For backup power that needs no starter battery at all, our Generac solar generator guide covers battery-based power stations.
FAQ
Are these batteries made by Generac?
No. They are third-party replacement batteries from Mighty Max Battery and Casil, sold as compatible with the Generac models they name.
What battery does a Generac GP7500 use?
The listings here that name the GP7500 or GP7500E are all 12V 9Ah sealed lead acid batteries.
Do I need to add water or acid?
No. These are sealed, maintenance-free SLA/AGM batteries.
Does the battery come with wires or a bracket?
The Mighty Max listings say battery only, with no wire harness or mounts; the 18Ah version includes screws.
Can I use the 18Ah battery instead of a 9Ah?
Only if it physically fits your generator. It is noticeably larger than the 9Ah battery.
