What is a solar battery tender?  A solar battery tender functions just like a regular battery tender except the power comes from the sun instead of an AC outlet.  Battery tenders are technically battery chargers, but in the case of a solar battery tender, it is more useful to keep a battery charged than it is to charge a dead battery.  That’s because the output power of a solar battery charger is so low.

So if you need to charge a dead battery or you want to charge a deep cycle battery, you would be better off buying a regular 12V battery charger or battery maintainer.  It will charge your battery at a much more reasonable rate and doesn’t depend on the sun for power.

Solar Battery Tender Solar Array ViewSolar battery chargers and maintainers are perfect for situations where the 12V battery is too far from the power grid to make plug-in power practical.  You might be storing an ATV, motorcycle, sports car or other seasonal vehicle in a shed or garage without power.  A solar car battery charger can keep the battery charged until you’re ready to use the vehicle.

What are some of the important considerations when buying a solar battery tender?


Typical solar battery tenders designed to charge and maintain 12V lead-acid batteries are rated at 5W, 10W, 15W and more.

The more often you need to use the battery you are charging; the more powerful a solar battery tender you need.  Battery tenders are mostly used for maintaining batteries and not charging dead ones.  If you need to charge the battery before it can be maintained and you will need the battery in short order, a more powerful solar battery charger can be used to charge the battery first and then maintain it until you need it.


Looking for other solar charger choices?  Be sure and see our other articles about some of the best!


If you leave a vehicle’s battery unused for long periods like over the winter, then you can get away with a smaller solar battery charger that only needs to maintain the battery until you use it again in the spring.

No matter which solar powered charger you choose, don’t expect it to perform like its plug-in counterpart.  A battery tender like Deltran’s Battery Tender Plus or Battery Tender Jr are going to perform faster and better, but they are useless without an electrical power source.

Charge Controllers

All solar panels that are used for battery charging need a charge controller between the panel and the battery to prevent overcharging.

Be careful when you are buying a solar battery charger because some solar panels are advertised as solar chargers, but don’t come with a charge controller.

Solar Battery Tender Earth Solar ViewYou need the charge controller and there are basically three ways to get it.  First, some solar panels come with built-in charge controllers designed specifically for battery charging and maintaining.  Second, you can buy a kit that includes both the solar panel and a matched solar charge controller in one package.  Third, you can buy the solar panel and the charge controller separately.

We recommend either buying a model with the charge controller built-in or buying a kit that includes a matched charge controller.  That way you don’t have to worry if the charge controller is designed to be used with the solar panel you’re buying and as important, there is probably some history out there of how successful the combination of charge controller and solar panel has been.

Smart Charging

Modern battery tenders come with built-in microprocessors that not only control the charging process, but also maintain the battery at peak performance using stages or phases that include reconditioning.  Not all charge controllers are designed to improve the health of your battery while connected.

Particularly if you’re planning to leave the solar charger connected for long periods, you should find a kit or solar panel that includes a smart battery tender that will take good care of your battery while connected.


All of the size of a solar battery charger is contained in the solar panel.  Charge controllers are very small and hardly take up any space.  It’s true that solar panels are thin, but it’s the area of the solar panel that takes up space.  With respect to power, if you want more power, you need a larger solar panel.  Unfortunately, solar panels don’t produce a lot of power, so it’s likely that if you want to use it as a solar panel battery charger, the solar panel will have to have some area to it.

Solar Battery Tender Sun ViewSafety

Most of the risk related to charging a lead-acid battery comes when you hook up the charger.  Lead-acid batteries can produce flammable fumes that may exist close to the battery.  If the connections spark when you connect the charger, those sparks may ignite the fumes causing an explosion.  To prevent this, smart chargers are designed not to produce a current until a proper connection is detected.  These connections are called spark proof.

Overcharging is another risk that can be overcome with a smart charger that monitors the battery’s charge and changes modes automatically without intervention from charging to maintenance or a float charge to maintain the battery.  Overcharging can cause damage to the battery and in a worst-case situation could cause the battery to explode.


It is common to want to mount the solar panel somewhere out of the way where it still gets enough sun to do the job.  Solar panels don’t have to be mounted.  You can lean them against a tree or building at a good angle pointing south towards the sun and they will work just fine.

The advantage of not mounting it is that you have complete flexibility in the angle and azimuth you choose to point the solar panel.  Ideally, the solar panel would move automatically in azimuth and change the angle to the sun so that it would always be pointing directly at the sun.  That would produce the most power.  The reality is that planetary mounts that can follow a point in the sky are expensive and you may not gain enough from using one that it would be worth it.

The solar panel battery tender we’re recommending comes with four holes in the corners of the solar panel where you could mount brackets to hang the panel from a wall or mount it to a roof.




The larger the solar panel, the less portable a solar battery charger is going to seem.  Most are fairly portable in that other than the panel, there isn’t much to carry and the combination of the solar panel and charge controller are very light.  Truly portable solar panels usually fold for the most compact storage and ease of transport, but expect to pay dearly for that functionality.

Temperature Compensation

Battery charging is essentially a chemical process that is affected by ambient temperature.  If you attempt to charge a battery and do not account for temperature, it’s possible to overcharge or undercharge the battery.  Cold batteries require a higher charge voltage and warm batteries a lower voltage.  Many smart chargers come with built-in microprocessors that can compensate for temperature.  This is especially important for battery tenders that may be left unattended charging and maintaining a battery in a variety of temperature conditions over a long period.


Solar cell manufacturing is not a perfect process and neither is solar panel assembly.  It’s possible to get solar panels with one or more faulty cells or cells that were improperly assembled into the panel.  To avoid having to replace a panel down the road due to manufacturing defects, get the longest warranty available.  Most solar panel chargers come with at least a 1-Year limited warranty.




We searched retail sites, forums, consumer sites, customer review sites, and manufacturer sites to find the best rated, most popular 15-watt solar battery tender out there.


Take a look at our choice and see if this is the best solar battery charger for your needs!


Battery Tender 021-1165 15W Solar Charger

Solar Battery Tender 15-Watt Solar ChargerOf the three choices for purchasing a solar battery tender, we recommend buying one with a built-in charge controller and that’s exactly the configuration of the Battery Tender 021-1165 15W Solar Charger.  It features a built-in 3-Step automatic microprocessor-controlled solar charge controller that is idea for charging and maintaining 12V lead-acid batteries.  If your battery is not convenient to electric power, then solar is a great choice and this model produces 15 watts of power to charge a battery faster than many solar chargers.

This solar charge operates in one of three primary charge modes:

  • Bulk Mode: Full charge power, constant current, increasing battery voltage, battery is 0% to 75 or 80% charged
  • Absorption Mode: High constant voltage, decreasing current, battery is 75 to 100% charged
  • Storage/Float Maintenance Mode: Low constant voltage, minimal charge current, battery is fully charged to 100 to 103%

A handy status indicator light provides information on a variety of battery charging conditions:

  • LED Flashing Amber:  Initially it means that the charger is functioning properly.  If the LED continues to flash amber it can mean that the battery voltage is too low to charge (less than 3 volts), the alligator clips are not properly connected (poor connection, reverse connection), or the battery is sulfated.
  • LED Steady Amber: A battery is connected properly and charging is in process.  The light will remain steady amber until the battery is approximately 80% charged.
  • LED Steady Green: Charge complete.

Safety features include spark proof connections and protection against short circuit and reverse polarity.  Here’s what you need to know.

Solar Battery Tender Features

  • 15-watt solar battery charger with unique built-in charge controller can charge 12V lead-acid batteries without an electrical power source
  • Smart, microprocessor-controlled solar charge controller with three charging modes
  • Safety features include spark proof connections, reverse polarity protection, and short circuit protection
  • Lightweight and portable
  • Waterproof setup is perfect for outdoor installations
  • Built-in temperature compensation sensor
  • A 5-foot lead to the panel and a 2-foot lead with alligator clips are included
  • Dimensions are 14W x 40L x 1H inches and it weighs in at 8 lbs.
  • 5-Year warranty




Battery Tender 021-1165 15W Solar Charger Documentation >>>




Solar Battery Tender Comparison


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