Anyone who leaves their car safely under covers during winter knows the value of a good car battery charger. Battery chargers and tenders keep your car’s battery topped up in a safe way over long periods of time. They’re great for folks who travel down south for the winter, or who have a classic or collectible car they only drive-in summer. Chargers are also useful if you order mail-order batteries that come shipped with the battery fluid not yet installed. Those batteries must be charged before you install them in your vehicle, though most modern batteries bought in store come pre-charged.
A trickle charger will slowly and safely charge a battery using preset charging rates. Many need to be disconnected manually once the battery is charged. A battery maintainer will test and monitor your battery over time, and only supply it with power when it needs to be charged. These are the “set and forget” type.
Maintaining a battery is better than boosting it at the end of the storage term because jump-starting can damage batteries, and the sensitive electronics in modern cars. If a battery drains too far, it can be impossible to boost. A new battery is expensive, especially if you buy one once every year or two.
As technology and manufacturing costs have improved the price gap between a tender and a charger has all but disappeared. Most battery chargers you will find on the market these days charge automatically and safely. Here are a few of our favourites:
1. Editor's Pick: Noco Genius10
Noco’s Genius10 all-in-one charger, trickle charger, maintainer, and battery desulfator provides safe, effective charging, and can even resurrect dying batteries.
It works with 6- and 12-volt lead-acid batteries in anything from cars and RVs to boats and motorcycles. The Genius10 is compatible with lithium-ion batteries as well as deep-cycle units. There are two big “wow factor” pieces in this product: the new-force mode, which will allow you to resurrect batteries as low as 0 volts in manual mode, and the battery desulfator that automatically reduces sulfur deposits on cell walls by pulsing electricity through them.
It also comes with a 12v supply mode, that converts the charger into a DC adaptor for powering 12v devices. The Genius10 will even work on batteries that have dropped to as low as 1 volt in automatic mode. At 10 amps, you can expect seriously fast charging capability, but safely. We also appreciate the generous 3.8m (12.4 ft) of available cabling.
This is a highly advanced maintainer that you can set and forget for months on end. An on-board thermal sensor compensates the charge rate according to conditions, so you don’t overcharge the battery in warmer weather or undercharge it in the winter. And, if you do forget to install it before you tuck your vehicle away for a while, the Noco unit will bring your now-dead battery back to life.
2. Most Reliable: Battery Tender Plus by Deltran
Deltran’s green-faced line of battery tenders is the image in most people’s mind when they think of a car charger. This clever-yet-simple device is perfect for long-term storage.
The company has been building high-quality, high-performance battery maintenance tools for a long time now, and they’re famous for simplicity and reliability. The 1.25amp smart charger will fully charge and hold that charge steady over time while regularly testing and cycling the battery to keep it healthy. The 10.5 ft of combined reach is handy, so too is the quick-connect wiring harness.
We appreciate the simplicity of the unit when it comes to use. The reverse polarity protection makes sure you’re safe, and the charging system compensates for rise and falls in the ambient temperature. It operates over four modes: Initialization, Bulk Charge, Absorption Mode, and Float Mode — all automatically. All you have to do is connect it to your battery, plug it in, and you’re done. Two LEDs on the front fascia tell you if the unit is charging or in storage mode, and flash if there’s a problem with the battery.
Battery Tender Plus is compatible with lead-acid, flooded or sealed maintenance free batteries. The downside is that it’s sensitive to low-voltage batteries. So if your battery has been drained completely this unit may not do the job. Still, it comes backed by a 10-year warranty.
3. Best Jump Starter and Battery Charger: Schumacher FR01336
This wheeled unit is capable of charging any lead acid battery and deep cycle batteries and offers automatic maintenance mode to keep batteries at their optimum. Schumacher’s FR01336 automatic battery charger also features up to 250 amps of jump-starting power to boost your car, SUV, or truck.
Schumacher’s FR01336 automatic battery charger also features up to 250 amps of jump-starting power to boost your car, SUV, or truck. It includes a battery and alternator tester, as well as reverse polarity lock outs to keep you safe.
The FRo1336 will automatically detect the voltage in your system, so you can use it safely on motorcycles or powersports equipment as well as on cars, trucks, and SUVs. Schumacher’s smart charger will also give you a reading on your alternator if you start the engine with it connected.
Schumacher offers even bigger jump starter and charger units but those are double the price of this handy little rig and are really only suited to car yards or mechanics who need to charge and boost on a regular basis. This is a great option for someone on a rural property with lots of equipment they use occasionally. It’s great value and comes in only a little bit above the non-boosting chargers in this list. It’s a cordless version, so you can’t leave it for long, but it’s a great short-term charger and tender.
4. Best Value: Stanley BC25BS
Stanley’s fully automatic bench battery charger and maintainer is an affordable and handy addition to your home garage. It also features a starting feature, but it’s not a genuine booster like the Schumacher unit above. Instead, it offers a quick-charging 75amp flow into the battery that quickly gets it charged enough for you to start your car. Stanley claims it will take batteries from drained to starting in 90 seconds, but it usually takes two to three minutes.
As well as that feature, the BC25BS offers 25 amp charging power for any deep cycle, lead-acid, Absorbed Glass Matt (AGM) or Gel batteries. That high amperage allows it to charge quickly — as much as 40 percent faster, according to Stanley. There’s also a top-off mode and a maintenance mode, both of which the device triggers automatically when it senses the battery is full or nearly full.
Four buttons on the front give you the ability to access the engine start and battery reconditioning features, as well as check the alternator and battery. The handy LCD display is great for those of us who want to know what’s going on and displays the charge level as you charge.
It’s not the cheapest possible charger, nor the cheapest on this list, but this cool little rig has all the right features and a compelling price point making it the best blend of versatility and cost.
5. Best Long-Term Storage Tender: Battery Tender Junior
Deltran’s entry-level battery tender is perfect for worry-free, long-term storage of your RV, car, truck, or motorcycle.
The second entrance in this short list from the same company earns its spot by being a no-nonsense, “does what it says on the box” example of a battery tender that you can get for less than a third of the price of other options here. It has a tiny power output, at just 750 milliamps (that’s half the amperage of your average smartphone charger), but that’s not the point. This is the charger you use on your classic hot rod parked in storage for six months of the year.
The Battery Tender Junior one only works on 12v batteries, but it works on all of them. Like its bigger brother above, the Junior features four-stage automatic charging to keep your battery at its optimum. It’s entirely self-contained, with an LED indicator that lets you know the state of the battery. We also like the generous cable length, and the ability to use alligator clips or ring clamps on the terminals.
If you have any vehicle that sits idle for months on end, the Battery Tender Junior will extend the life of your battery and pay for itself many times over in no time.
How Do You Charge a Battery?
Some battery tenders require you to disconnect and remove your battery from your vehicle altogether, others allow you to leave the battery installed and connected. Check the instructions on your charger before proceeding. We advocate disconnecting the battery in any case and find it’s best to pull it out of the vehicle. The reason is that the charging process can cause your battery to emit hydrogen gas, even at low trickle-charge levels, which can be dangerous. That’s also why you shouldn’t charge your batteries inside your home but rather in the garage.
If you are disconnecting your battery, always remove the negative lead first. It is always the first to disconnect and the last to connect. That’s because once the negative terminal is disconnected it’s almost impossible for you to short the circuit while working to remove the positive lead — save by touching your wrench to the negative terminal and positive terminal at the same time.
If you’re working on the positive terminal and you touch the tool to the bodywork or any other engine parts, you’ll create a circuit, which is bad for the battery, and the car’s electronics.
So, negative cable — first off, last on, always. The same is true when it comes to connecting up your battery charger, the negative goes on last.
So, to charge a battery, always follow these steps:
- 1. Connect the positive charger cable to the positive battery post
- 2. Connect the negative charger cable to the negative battery post
- 3. Plug the charger into the wall and turn it on
To disconnect the battery charger:
- 1. Unplug the charger
- 2. Disconnect the negative terminal
- 3. Disconnect the positive terminal
Can a Battery Charger Resurrect a Dead Battery?
Sometimes a battery is just dead; and, sometimes a battery is at zero, but it’s not quite dead. Chargers like the Noco unit in this guide can be used to force-charge a battery from zero volts, but that’s only half the story. As the battery loses charge, sulfur deposits can form on the walls of the battery cells. This is mostly only a problem for traditional wet cell batteries.
That’s when a desulfator does its work. Chargers that have desulfurization properties send powerful electric pulses through the battery, which effectively “wakes up” those sulfur deposits, which dissolve back into the acid. This process can bring back batteries that testers say is dead, and greatly prolong the life of older, neglected batteries - especially those that have been allowed to lost charge over time.
How Do You Know When a Battery is Dead?
All the tenders in this list will indicate if the battery they’re charging isn’t taking the charge. When that happens, you may need a new battery. In some cases, you can try a force-charge and desulfurization (which is why we like the Noco Genius10 so much) – but if your battery still refuses to hold charge or take a charge, it’s time for a new one.
You can also test to make sure your alternator is working correctly with some of the products listed above. If you know how to use a multimeter, or if your car is equipped with a voltage gauge, you should see a reading of between 13 and 14 volts when the engine is running. Any less than that, and your alternator is likely the issue. If that number is inconsistent, that also points to the alternator.
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