Generac battery - Charging, testing & replacement guide

Generac, Guardian, Honeywell, Siemens, Centurion, Watchdog, Bryant, & Carrier Air Cooled Home Standby generator troubleshooting and repair questions
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Chris
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Wed Dec 05, 2018 8:35 pm

I'm just going to do a quick overview of how you properly test a battery in a Generac generator of any size (this also goes for any battery in a generator in most cases).

If you're having charging problems to the point that the battery is going dead and having to be re-charged manually with another charger, you should address the charging issues FIRST before trying to diagnose a bad or dead battery. If you can't keep the battery charged, that is your first problem...

You can test for battery voltage right at the battery terminals using a quality digital volt meter (I list an example below of the Fluke 115). The voltage on the terminals of a charged or charging battery should be between 13Vdc and 14Vdc +- about .5 volts. If you're getting more or less than that, you may have charger issues and the charger should be inspected. A fully charged battery that has sat without a charger on it will measure about 12.7Vdc (a new store bought battery).

On newer Evolution model and Nexus model generators, the chargers are built into the controller making troubleshooting a little bit more difficult. The easiest way to test a charger is to measure battery voltage before starting the unit, record the value, start and stop the generator, and then monitor the battery voltage. The battery should have been slightly depleted by the starter and you should be able to watch the charger making the voltage of the battery increase back to where it was before the start.

If you are seeing normal voltage at the battery terminals but the unit still acts like it has a dead battery, the charger most likely is fine and the battery has gone bad. All too often I get told by someone troubleshooting that the voltage looked good on the battery but it still won't crank. What they haven't done is load tested the battery. A bad battery will show normal voltage in a lot of cases because the charger is working, however when the starter is engaged, the voltage may drop to almost 0 because the battery has no capacity to actually carry the load that the starter is applying to it.

The best and easiest way to properly test a battery is to load test the battery. This is done using a very inexpensive battery load tester (shown below) which applies a resistive load to the battery in the form of a heating element. When the load is applied to the battery, a good battery will drop slightly to around 11.5Vdc but then recover back to normal voltage after a few minutes. A bad battery will drop significantly to a much lower voltage, maybe even 0. This indicates a bad battery and it should be replaced.

If the battery tests good and you still have starting problems, move on to the next logical step in troubleshooting. This depends on the generator model. If you need more help, please start a new topic with more specific details about the problem.

The battery for a Generac Air Cooled generator in almost all cases is a Group 26. A battery any larger than this may not fit and a battery smaller than that may have issues starting the generator. You should be able to find a replacement battery at a local auto parts store, or your local Generac Dealer.

Some tools you'll want to have on hand for battery testing:

Battery load tester
https://amzn.to/2rnZwrv
Battery-Load-Tester.jpg
Battery load tester for generators
Battery-Load-Tester.jpg (65 KiB) Viewed 5647 times
Fluke 115 Meter
https://amzn.to/2rn0OmL
Fluke-115-Meter.jpg
Fluke 115 digital multi meter
Fluke-115-Meter.jpg (48.97 KiB) Viewed 5647 times
Generac tech for over 12 years. I'm here to help!
"The only source of knowledge is experience" -Albert Einstein
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78buckshot
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Thu Dec 06, 2018 5:35 am

Chris, this is a good guide. Much of what you wrote is the testing that I do when performing PM's. I read and record float voltage when I first get to the site because that will tell me what the charger is doing, then cranking voltage for a couple of crank cycles with the gas turned off, and running voltage while warming the engine before changing the oil.
Birken Vogt
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Thu Dec 06, 2018 11:15 am

Exactly. Measure voltage when going on site before doing anything. Should be > 12.8 or > 13.0 depending on charger in use. Turn off gas and crank engine for one long crank cycle. A good battery will show > 11.0 for the whole cycle. Usually they will drop to something like 11.4 for a few seconds, then rise up a few tenths as the battery warms. The starter should be cranking energetically for all this time.

Battery replacement every 3 years, non-negotiable. The battery is the most critical point in the system. If the battery is out they have nothing when the power goes out. We don't wait for it to fail before replacing it and they seldom give any warning before failing.
Gentexx
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Mon Dec 24, 2018 5:48 pm

A lot of people need this!! Nice job. Keep it up.
Chris
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Mon Dec 24, 2018 6:03 pm

Thank you! :bigsmile:
Generac tech for over 12 years. I'm here to help!
"The only source of knowledge is experience" -Albert Einstein
Looking for Generac parts? Gentek Power offers the full line of Generac replacement parts! Shop Gentek Power Generac Parts
A list of my favorite Generator & Electrical Tools! https://www.amazon.com/shop/gentek_power
Louispc
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Sun Jul 21, 2019 10:18 am

I have a model 0G3506.

The unit is not charging the battery. I checked the fuses there good. I checked the transformer in the breaker panel I have 16vdc.

Then I went to the unit outside, I checked the voltage coming into the transformer, it reads 240v

On terminals output. 9 and 10 on the transformerI have no voltage either the wires 224 and 225. With the unit not running.

When I unplug the wires on the transformer on post 9, 10, I’m getting 16v.

Could the solid state Battery Charging unit 0A18010SRV be bad?

How can I do a test on the 0A18010SRV to determine if it’s bad or not.

The Battery is brand new by the way,

Please let me know you thoughts. Thanks
Chris
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Sun Jul 21, 2019 10:37 am

Louispc wrote:
Sun Jul 21, 2019 10:18 am
I have a model 0G3506.

The unit is not charging the battery. I checked the fuses there good. I checked the transformer in the breaker panel I have 16vdc.

Then I went to the unit outside, I checked the voltage coming into the transformer, it reads 240v

On terminals output. 9 and 10 on the transformerI have no voltage either the wires 224 and 225. With the unit not running.

When I unplug the wires on the transformer on post 9, 10, I’m getting 16v.

Could the solid state Battery Charging unit 0A18010SRV be bad?

How can I do a test on the 0A18010SRV to determine if it’s bad or not.

The Battery is brand new by the way,

Please let me know you thoughts. Thanks
It's very possible that the charger is bad. You can test for AC voltage on the input wires at the top of the charger (the smaller 2 wire connector) and should read around 19 VAC. The output is measured in DC voltage and will be the larger 3 wire connector that only has to wires (no wire in the middle spot). Output should be around 13.5 VDC on those 2 wires. If you have AC input and no DC output, the charger is bad. I have one in stock here if you need. https://shop.gentekpower.com/products/g ... 6bfd&_ss=r
Generac tech for over 12 years. I'm here to help!
"The only source of knowledge is experience" -Albert Einstein
Looking for Generac parts? Gentek Power offers the full line of Generac replacement parts! Shop Gentek Power Generac Parts
A list of my favorite Generator & Electrical Tools! https://www.amazon.com/shop/gentek_power
TAB
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Thu Oct 10, 2019 6:50 pm

I would like to mention to routinely check the electrolyte levels in the battery, add distilled water only to bring levels up. 12v batteries have six separate cells, wear eye protection and add distilled water until you see the water “Pucker” in the port, there is a slotted tube that extends into the battery that when the water level touches the bottom of the tube the reflection of the water will distort or “pucker” to show correct level, the tube is slotted all the way to the top to allow hydrogen gas to vent off, but fill to just the bottom of the tube. If you run the electrolyte level too low you risk uncovering the plates and the battery deteriorates rapidly. Generac recommends checking yearly.
bmeyersadvisor
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Sat Nov 09, 2019 6:43 pm

I have a 17k model 0055050

Just replaced the 10 year old battery. It will not stay charged. Can you walk me through a diagnostic test to determine the failed part?
Chris
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Mon Nov 11, 2019 8:33 pm

bmeyersadvisor wrote:
Sat Nov 09, 2019 6:43 pm
I have a 17k model 0055050

Just replaced the 10 year old battery. It will not stay charged. Can you walk me through a diagnostic test to determine the failed part?
The failed part will most likely be the battery charger in the transfer switch. You can find the charger here: https://shop.gentekpower.com/products/g ... connectors

Basically the charger has 120V power in, and 13.5VDC output. They were a common failure, especially after 10 years.
Generac tech for over 12 years. I'm here to help!
"The only source of knowledge is experience" -Albert Einstein
Looking for Generac parts? Gentek Power offers the full line of Generac replacement parts! Shop Gentek Power Generac Parts
A list of my favorite Generator & Electrical Tools! https://www.amazon.com/shop/gentek_power
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