The Solar Power Expert Blog

Deep Cycle Battery Charger Reviews

by Chris - December 8th, 2011.
Filed under: Equipment. Tagged as: , , .

Although most off-the-shelf 12v chargers today are designed to respect deep cycle battery charging rules, it always helps to know what to look for when buying a deep cycle battery charger. This post will point out the important features to look for in a battery charger to ensure you get the longest life from your 12v deep cycle battery. I will also recommend a charger that I have personally used for years. Weather your a solar enthusiast or not, a good, quality battery charger is an essential tool to have around the house.

Deep Cycle Battery Maintenance

Most people associate AGM batteries with deep cycle batteries. This is because AGM deep cycle batteries have superb deep cycle life. However, it is possible to have flooded cell deep cycle batteries as well as AGM starting batteries. For this reason, it’s important to know what type of batteries you’re talking about. To be clear (and for the sake of this discussion), I want to point out that I am speaking of Sealed Lead Acid (SLA) batteries. These are also known as valve regulated lead acid (VRLA) batteries or maintenance free batteries. These include all AGM and gel batteries.

These are all batteries that are designed not to vent gas. They are sealed. This is in contrast to flooded cell batteries in which oxygen is allowed to enter and exit the battery.

If an SLA battery is improperly charged, it will vent gas which will damage the battery. So picking the right charger is crucial. However, picking the right deep cycle battery charger is the only deep cycle battery maintenance that you need to do. Hence the term, maintenance free.

Gel Deep Cycle Battery Chargers

Gel batteries need special charging considerations. The most important consideration is that they need to be trickle charged at 14.1 volts while other batteries should be trickle charged at 14.4 volts. For this reason, marine gel batteries (and other types of gel battery for that matter) need to have a special charger. If you are using gel batteries, then make sure the charger says ‘gel battery friendly’ on the packaging somewhere.

How to Charge a Deep Cycle Battery

According to this East Penn Technical Manual, it’s crucial to pick a charger that is ‘voltage regulated’ or ‘voltage limited’ in order to prevent gassing.

Ideally, the charger should also adjust its charging voltage with temperature in order to compensate for the battery. This is a nice feature, but not critical. Most chargers will float the voltage to 14.4 volts to maintain the battery. If a small deep cycle battery charger advertises temperature compensation, then check the details. The temperature inside the battery can be quite different than the ambient temperature, so bear that in mind. However, most chargers don’t compensate for temperature. Here are a few tables from the East Penn Technical Manual of how charging voltage should compensate for temperature:

How To Charge A Deep Cycle Battery

SLA Charging Voltages vs Temperature

Deep Cycle Battery Chargers

I reviewed several battery chargers that are available on for use as a deep cycle battery charger. My top pick is the Black & Decker 10/6/2 Amp Charger. However, I found several application specific battery chargers that made me stop and go, “Wow! Cool!”.

Black & Decker 10/6/2 Amp Charger

I have personally used this charger for several years and it has worked great. However, if you look through the Amazon comments, you’ll see people complaining that the charger is ‘too’ smart.

One of the features I like the best about this charger is that you can switch the display back and forth to monitor both battery voltage and charging current. You can also adjust initial charging current for 2, 6, or 10 amps, which makes it idea for charging even small deep cycle batteries. As the battery approaches full charge, this charger automatically tapers off the current and maintains the batteries at precisely 14.4 volts. You can see for yourself (from looking at the display) that your batteries are being charged as fast as is healthy.

Schumacher 1.5A Automatic Battery Charger

This charger was one that made to stop and go ‘Oh, cool!’. It’s intended to be used on vehicles that aren’t used very often – be it a car, boat, ATV, motorcycle, etc. In fact, it’s intended to be mounted on the vehicle, near the battery. When you store your vehicle, you simply plug the end into an extension cord to ensure that the battery is properly maintained during storage. This is an ideal solution for a small boat, RV, or motorcycle that is used infrequently.

It’s safe for all deep cycle batteries due to it’s ‘automatic’ charging capability to regulate charging voltage. This ensures that the battery is not overcharged – a significant difference from the old school trickle chargers that put out a constant 1.5 amps. Those older types of charger could fry small deep cycle batteries.

Battery Tender

The Battery Tender has long been a favorite among people who care about their batteries. This little device has won over customers for years. The manufacturer is also willing to put their money where their mouth is by offering a limited 10-year warranty.

This device is one of the few battery chargers that are truly temperature compensated – however keep in mind that it uses the ambient temperature and not the batteries internal temperature. The charge rates are so low (1.25 amps), that there shouldn’t be a significant difference between the temperatures. (The customer reviews seem to indicate that the product works great too.)

It’s also possible to configure this charger for use on Gel batteries. If you have thought about the merits of Gel batteries for deep cycle applications and want to get your feet wet, this charger can do all types of lead acid. Even if you don’t buy this charger, it’s worth studying the product literature to find out what makes a good quality charger and how to charge a deep cycle battery.

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