Generator Battery Chargers: Types and Sizing

Why a battery charger matters for your generator

Generators with electric start rely on a 12-volt starting battery. If that battery runs low, the electric starter may not turn the engine over, and you may have to use the recoil cord instead. A battery charger keeps the battery ready between uses, especially if the generator sits for weeks or months. For a portable generator used only during outages, a charged battery means you can start it quickly when the power goes out.

This article explains the types of chargers you may see on listings or as separate purchases, and how to choose one for your situation. It does not cover wiring or installation; a licensed electrician and the maker's manual decide those details. If you are comparing generators, read the listing to see whether a charger is included or sold separately.

Types of battery chargers for generator batteries

Trickle chargers deliver a low, steady charge to keep a battery topped up over long periods. They are simple and often inexpensive, but they may not adjust for temperature or battery condition. A trickle charger can be left connected for weeks, but you should follow the charger maker's instructions to avoid overcharging.

Smart chargers, also called automatic chargers, monitor the battery's state and adjust the charge rate. They can switch between charging and maintaining, which helps avoid overcharging. Many smart chargers work with lead-acid batteries, including AGM and gel types. This makes them a versatile choice for most generator starting batteries.

Battery maintainers are similar to smart chargers but are designed mainly to hold a battery at full charge rather than to recharge a deeply discharged battery. They are a common choice for seasonal storage. If you store your generator for the winter, a maintainer can keep the battery ready for spring.

Some generators include a built-in charger that works when the engine runs or when connected to household power. Read the listing to see if a charger is included or if you need to buy one separately. For example, many inverter generators with electric start include a charging port or a built-in maintainer.

• Trickle charger: low, steady charge for long-term storage
• Smart charger: adjusts charge rate, prevents overcharging
• Battery maintainer: keeps a battery at full charge
• Built-in charger: included with some electric start models

How to size a charger for your battery

Chargers are rated by their output in amps. A higher amp rating charges a battery faster, but a charger that is too large for a small battery can overheat it. A lower amp rating, such as 1 to 2 amps, is often enough for maintaining a generator starting battery. For a small camping generator, a 1-amp maintainer is usually sufficient.

The right size depends on your battery's capacity, which is measured in amp-hours (Ah). The battery's label and the maker's manual state this figure. Match the charger's output to the battery's needs, and follow the charger maker's guidance for your battery type. If you are unsure, contact the generator maker or the battery manufacturer.

For a generator that is used only occasionally, a low-amp maintainer is usually enough. For a battery that has been deeply discharged, a smart charger with a higher amp rating may be needed, but check the battery's specifications first. A dual fuel generator may have a larger battery if it has remote start, so read the listing for battery details.

What to look for in generator listings

When shopping for a generator, read the listing for battery-related details. Some listings mention a battery charger, a battery tender, or a maintenance mode. Others may not state the charger type at all; in that case, check the maker's page or the manual. Look for terms like 'battery included' or 'charger included' to know what you are getting.

Look for the battery type the generator uses, such as lead-acid or AGM. This affects which charger is compatible. Also note whether the generator has electric start, remote start, or both, as these features draw from the same battery. A whole house generator may have a larger battery and a more robust charging system.

If a charger is not included, you may need to buy one separately. Consider a smart charger or maintainer that matches your battery type and the generator's voltage, which is typically 12 volts. For an RV generator, the charger may need to be compatible with the RV's battery system, so read both manuals.

Caring for the starting battery

Keep the battery terminals clean and free of corrosion, as the maker's manual describes. Check the battery's charge level regularly, especially before storm season or a camping trip. A simple voltmeter can tell you if the battery is low, but the manual will explain the proper procedure.

If the generator has a battery disconnect switch, use it when the generator is stored. This reduces the drain on the battery from clocks, memory circuits, or other small loads. For a camping generator that is used a few times a year, disconnecting the battery can extend its life.

Follow the maker's manual for charging intervals and storage conditions. The manual may recommend a specific charger type or a maintenance schedule. When in doubt, contact the maker. Keeping the battery charged is part of routine care, just like checking the oil or the air filter.

Safety notes for battery charging

Batteries produce hydrogen gas during charging, which can be flammable. Charge batteries in a well-ventilated area, away from sparks or flames. Read the charger's instructions and the battery's warnings before connecting. Never charge a battery that is cracked or leaking.

Use the correct charger for your battery type. Using the wrong charger can damage the battery or create a hazard. If you are unsure, ask the maker or a qualified technician. Do not attempt to modify a charger or the generator's electrical system.

For generator use, always follow the CPSC guidance: never run a portable generator indoors or in garages, basements, or sheds. Use it outside, away from windows, doors, and vents. Read the CPSC's carbon monoxide safety pages for more information. This applies to any generator, whether it has a battery charger or not.

What to pick for your situation

Questions

Do all generators with electric start include a battery charger?

No. Some generators include a built-in charger, but others require a separate charger. Read the listing and the maker's page to see what is included. For example, some portable generators come with a battery tender, while others do not.

Can I use a car battery charger on my generator battery?

You can, but only if the charger is compatible with your battery type and voltage. A car charger may deliver too high an amp rate for a small generator battery. Check the battery's specifications and the charger's instructions. When in doubt, use a charger designed for small batteries.

How often should I charge the generator battery?

Follow the maker's manual. In general, check the charge level monthly and charge it before use, especially after long storage. A maintainer can keep it topped up automatically. For seasonal storage, a maintainer is a good investment.

What is the difference between a trickle charger and a maintainer?

A trickle charger delivers a constant low charge, which can overcharge if left connected too long. A maintainer monitors the battery and stops or reduces the charge when full, making it safer for long-term use. For most generator owners, a maintainer is the better choice.