How to Charge a 12V Battery: Important Battery Tender Maintenance

How to Charge a 12V Battery: Important Battery Tender Maintenance

When you ask how to charge a 12V battery, your next question could be how to maintain a 12V battery.  Most folks are familiar with battery chargers that canHow To Charge a 12V Battery NOCO Genius G3500 On Car View charge a car battery, but are not as familiar with battery tenders.  You really can’t learn how to charge a 12V battery without also learning about how to maintain your battery once it is fully charged.

When you learn how to charge a 12V battery, you will know how to bring the battery up to a full charge.  Once it’s fully charged, how do you keep it charged when it’s not in a vehicle that will keep it charged?  You will do that with a battery tender or battery maintainer like the Battery Tender Plus or NOCO Genius G3500.

Battery Tenders

A battery tender is a device that you can use to plug into your standard AC outlet to charge and maintain your 12-volt auto battery or other vehicle battery.  Although it charges auto batteries and other vehicle batteries, almost as important is its ability to maintain and even repair batteries.  Modern battery tenders may be able to handle charging and maintaining both lead-acid and lithium-ion batteries.  This article is about lead-acid battery charging.


Interested in buying a battery tender?  Here are some of the best available:


How To Charge & Test Your Car Battery

Modern battery tenders are microprocessor controlled and use multi-step charging programs to charge, maintain, and repair your battery.  Many of them are set-and-forget chargers that can perform all their functions automatically without any intervention on your part.  This is particularly helpful when you are storing a vehicle for the winter or only use a vehicle periodically.

Storing A Car Battery Properly Video

Modern battery tenders not only provide an electrical charge to the battery, but also detect the charge state of the battery in order to provide just what the battery needs.

The good news is that if you buy a computer-controlled battery tender, the steps for how to charge and maintain your battery are easy.

Battery Tender Usage

How To Charge a 12V Battery NOCO Genius G3500 Front ViewFor most batteries you simply plug in the charger, hook up the leads to the proper battery terminals, and start the charger.

Plug-in the charger to any regular household 110-120V outlet.  If you need to use an extension cord, you will need to be concerned with the length of the cord.  Consult your battery charger manufacturer’s extension cord wiring requirements.

Connect the leads to the proper battery terminals.  Red connects to red, and black connects to black.  Some battery tenders have built-in reverse-polarity detection so even if you hook them up wrong, the battery tender will detect the problem and warn you.

That’s how you start charging, but what does a battery tender do next?

Battery Tender Program

Most battery tenders follow a program that performs the following steps or steps that are similar:

Qualification or Initialization Mode

It is during this step that the battery charger measures the connection between the battery and the battery charger output.  Two primary problems that the charger can detect are when the charger output is positive, but the output current is zero.  This can happen when there is a bad connection between the charger and the battery that can occur when a fuse blows.  The second problem is when the output voltage is positive, but the output current is negative.  This could happen when the connections to the battery are improperly reversed.  Your battery tender may or may not have the ability to detect these conditions and present an error condition.

Recovery Mode

Some battery tenders have the ability to recover severely discharged batteries that normally cannot be charged by a standard battery charger.  This can happen when you forget to turn off your lights or leave some other electrical device running after the vehicle is turned off.

In that case, the battery tender will attempt to use low current to build up the battery’s charge slowly over time to the point where it can accept a charge.How To Charge a 12V Battery Battery Tender Plus Front View


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Bulk Charge Mode

It is during this step that the heavy-lifting is performed by the charger.  Most chargers have a maximum time that they can remain in bulk charge in order to prevent damage to the battery.  Modern battery tenders will charge the battery during bulk charge until the battery is fully charged and then automatically move to the next step in the program.  In some instances, when something is wrong with the battery, it will not reach full charge within 72 hours and the battery tender will stop the process.  Most battery chargers will charge the battery to approximately 80% of capacity during the bulk charge mode.

Absorption Mode

Absorption mode is designed to bring a battery up to full charge without damaging it.  If you continued in bulk mode to try and fully charge a battery, the amount of current might damage the battery.  So in this mode, voltage is held constant while current is allowed to decrease over time until the battery is fully charged.

Float/Maintenance Mode

How To Charge a 12V Battery Schumacher SC-10030A Front ViewFloat/Maintenance mode is designed to maintain a battery at full charge by detecting the battery’s charge state and providing a minimal charge when the battery’s charge voltage falls below a certain level.  Most modern battery tenders will operate automatically and independently to maintain the battery’s charge indefinitely without damage to the battery.

Remember that battery tenders are different from traditional trickle chargers which are not automatic and must be monitored to prevent overcharging.

Some of the best battery tenders available are from NOCO Genius, Battery Tender, Schumacher, and CTEK.






Battery Tender Comparison Chart

TitleCTEK 93-56-864 MUS 4.3 Black 12V Battery ChargerCTEK Multi US 3300 12-Volt Smart Battery ChargerBattery Tender 021-0123 Battery Tender Junior 12V Battery ChargerBattery Tender 021-0128 Battery Tender Plus 12V Battery ChargerNOCO Genius G3500 6V/12V 3.5 Amp Smart Battery Charger and MaintainerNOCO Genius G7200 12V/24V 7.2 Amp Smart Battery Charger and Maintainer
Warranty5 years5 year material and workmanship10 year material and workmanship5 Year Limited Warranty5 Year Limited Warranty
Height1.5 inch9 inch11 inch4 inch3.4 inch
Weight1 pound1.8 pound2.3 pound2.65 pound3.5 pound
Width2 inch4 inch4 inch10 inch11.7 inch
Length6.5 inch8 inch11 inch10.5 inch13.2 inch
Rating0 out of 5 stars0 out of 5 stars0 out of 5 stars0 out of 5 stars0 out of 5 stars0 out of 5 stars
ReviewsRead ReviewsRead ReviewsRead ReviewsRead ReviewsRead ReviewsRead Reviews
LinkMore InfoMore InfoMore InfoMore InfoMore InfoMore Info

Product prices and availability are accurate as of Jun 11 3:03:54 UTC but are subject to change. Any price and availability information displayed on the merchant site at the time of purchase will apply to the purchase of this product.

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Do you feel more comfortable using a battery charger or tender?  Which battery tender are you planning to buy? Please take a moment to leave a comment below.

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There you have it; how to charge a 12V battery using a battery tender.  We sincerely hope that this article has provided you with valuable information about how to charge a 12V battery!

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