Read the manual thoroughly and understand all of the instructions, cautions, and warnings before using this equipment. If any section of the manual is not understood, contact your nearest authorized dealer, or contact Generac Customer Service at 1-888-436-3722 (1-888-GENERAC), or www.generac.com with any questions or concerns.
Selecting and replacing a battery for a home standby generator
Selecting the right battery for your generator and understanding how to replace it are crucial for maintaining its efficiency and longevity. This article guides users on home standby generator battery selection and replacement.
Note: New home standby generators do not come with a battery, which must be purchased separately.
Environment
This article applies to the Generac air-cooled home standby generators pictured below.
Next Gen
Guardian
PowerPact
If you have a Next Gen series generator, the battery requirement is: 12‑volt, AGM Powersport Battery Group BTX20L 310CCA minimum.
If you have a Guardian series generator, the battery requirements are: 12‑volt, Group 26R 540 CCA or Group 35 AGM 650 CCA.
If you have a PowerPact generator, the battery requirement is: 12‑volt, Group U1 Exide Battery 300 CCA minimum.
Click here for individual battery part numbers, where applicable.
Home standby generator battery specifications
Voltage
Air‑cooled home standby generators require a 12‑volt DC battery to function correctly.
Cold Cranking Amps (CCA)
CCA measures a battery’s ability to start an engine in cold temperatures. The higher the CCA, the better the battery will perform in colder climates.
Understanding battery group type and CCA
- The 12V Group 26R 540 CCA battery is commonly used in Generac home standby generators for its reliable starting power and performance in various temperatures.
- The "CCA" rating indicates the battery’s ability to start an engine at 0°F (‑18°C) for 30 seconds while maintaining a voltage of at least 7.2 volts.
- The "Group 26" designation for the battery specifies physical dimensions (approx. 8.2" L × 6.8" W × 7.8" H).
- The "R" in 26R denotes "Reverse" terminal polarity, important for proper fit and connection in the generator system.
- Incorrect terminal orientation can cause cable routing issues and unsafe installation.
Guardian series:
- Group 26R 12V 540CCA: 0H3421S
- Group 35 AGM 650 CCA: N/A
Next Gen series:
- Group BTX20L: A0002359535
PowerPact:
- Group U1 Exide Battery: 0J5584
Note: Always consult your generator’s Owner's Manual for battery specifications. For further assistance or battery recommendations for specific geographical areas, contact a local Independent Authorized Service Dealer (IASD).
Where to purchase
Replacement batteries can be purchased at automotive stores, specialized battery stores, or from authorized Generac dealers that sell generator accessories and parts.
Battery replacement
Battery disposal
Dispose of batteries according to state and local regulations. It is essential to follow all guidelines to prevent environmental harm.
Additional battery and battery charger facts
- Home standby generators can use either flooded lead acid (require distilled water) or AGM batteries.
- Battery charging on home standby generators is accomplished with a built‑in Automatic Float Charger. This type of charger will safely charge the battery to full charge, then reduce the charge rate to the minimal amount of power needed to keep the battery charged and support the power needed for the engine control board (will not overcharge the battery).
- To learn more about the charging system, see Understanding the Home Standby Generators Charging System.
Comparing battery types
Group 26R vs Group 35 AGM (Guardian series)
- For Guardian series home standby generators, either Group 26R or Group 35 AGM are acceptable batteries.
- 26R is a wet cell and 35AGM is absorbent glass mat.
- Group 26R batteries are commonly used in home standby generators, however, Group 35 AGM batteries may be desirable for generators that are installed in cold environments, as they have a higher CCA.
- To learn more about the recommended battery for your installation, we recommend contacting a What Battery Do I Need for My Home Standby Generator?
Marine batteries
- There is no benefit in using marine batteries in home standby generators.
- Marine batteries typically cost more but perform the same as automotive batteries. In some cases, they are designed for ease of connection in a boat application.
- There is also a specialized marine battery called a “Deep Cycle Marine Battery”. Again, a more expensive battery. The primary use is for deep cycle marine batteries is electric trolling motors and is designed to better survive multiple charge and discharge cycles.
Lead‑acid batteries: Wet cell vs. gel cell
- The most common type of generator battery is a wet cell lead acid battery. This simply means that the electrolyte (acid) is a liquid.
- There is a less common gel cell lead acid battery. The acid in this battery is in a gel state. They are commonly used in applications where the battery can tip over.
Common questions
What is an electrolyte?
The electrolyte is the acid in a battery. As mentioned above, it can be in a liquid or gel state. The electrolyte (acid) is put in the battery at time of battery activation and never added later. If a wet cell is low on electrolyte, only distilled water can be used to top off.
Note: Most batteries are Sealed Lead Acid Batteries. This type of battery is considered a no maintenance battery and should never lose electrolytes.
Is the red terminal (cable) always positive?
This is not written in stone, however, red cables and terminals typically will be positive.
In what order do you disconnect and connect the battery cables?
When disconnecting, start with the negative cable first. When reconnecting, connect the positive first, then the negative.
What battery is recommended for cold environments?
For generators installed in cold climates where the temperature regularly drops below 32°F or 0°C, a battery with a higher CCA (like the Group 35 AGM) is recommended to ensure ample starting power.
Alternatively, generator owners can use a Group 26R battery and purchase a battery warming mat to help the battery start the generator in cold environments: What are the cold weather accessories for my home standby generator?
See Also
