A Battery Maintainer Saves Your Car’s Battery During Storage

Standard battery chargers are meant to revive dead batteries and get you back on the road. They shouldn’t be hooked up long-term. A battery maintainer (or tender) also recharges batteries. But a maintainer then goes into maintenance (or float) mode for cars in storage.

A battery maintainer often costs less than $30. It’s an excellent investment to top off your battery and then “trickle” charge through the winter.

I found out what can happen without one. I rented a garage to over-winter one of my collector cars. The landlord was upset when she saw I had it plugged in. She envisioned big electric bills.

I tried to explain that the battery maintainer operates at low voltage and barely uses any energy. It comes on only when necessary to maintain the charge of the battery. She wasn’t convinced.

After a cold winter unplugged, the formerly good battery was dead and buying a new one cost me $120. That could have been avoided.

Battery Maintainer Amperage

All battery maintainers do the job of keeping a battery charged. They use sensors to detect the battery’s state-of-charge. When the level dips below a threshold, the charge starts to trickle.

Our list of battery maintainers below use amperage that varies between a half-amp to three amps. Higher amperage means faster charging rates.

Higher amps is only required to speed up the charging of a dead battery. But lower amperage—just a single amp or so—is sufficient for a battery maintainer. That said, battery maintainers with higher amps usually don’t cost much more.

Many battery maintainers allow you to designate either six or 12 volts. But nearly all modern cars use 12-volt batteries. However, some older classic cars and other types of vehicles use six-volt batteries.

Here are a few common battery maintainers and other features they offer.

Shop now for battery maintainers and tenders

Black + Decker BM3B
$20 to $30

The BM3B 1.2-amp unit has a light that blinks green to tell you it’s working. Like many of these units, it warns of short-circuiting and reversed polarity (hooking up the terminals to the wrong connections). That’s a critical safety feature for any battery maintainer. Batteries connected to power the wrong way around can explode.

The Black + Decker clips are on the small side and can pop off the terminals if not set carefully. However, there are also O-rings for a more secure connection. The BM3B also offers this beneficial feature: “AC low-voltage compensation ensures maximum performance when used with an extension cord.”

Reviewers say that, if used in damp conditions, it may be prone to circuit-board corrosion.

Delran Battery Tender Plus
About $50

This unit charges at 1.25 amps, then goes into battery-maintenance mode. The Delran Battery Tender Plus is switchable to six or 12 volts. It has 50 percent more charging power than the same company’s cheaper Battery Tender Junior. That can be important when you first hook up the unit and want it to quickly get your battery back up to full charge.

It’s spark-proof and detects reversed polarity.

Duralast Battery Maintainer
Around $40

The Duralast device can charge at up to two amps. The battery maintainer automatically adjusts the amperage to maintain the battery. It also automatically detects six- or 12-volt batteries. The clamps are large enough to get a firm hold on the terminals, and O-rings are included.

A light indicates charging status, and there’s a “bad battery” warning. A handy hook folds out and allows you to hang the unit from the car’s hood.

Ferrari Battery Maintainer and Conditioner
From $99 to $250

This Ferrari battery charger is designed for your dormant Ferrari and priced like it. The manufacturer promises an eight-step automatic charging program, unique reconditioning mode, and built-in temperature sensing. But some of the lower-priced units have that, too.

Moto Power battery maintainer

Moto Power MP00205A
About $20

Moto Power offers one of the cheaper units, but it has plenty of features. It protects against over- and under-charge and will tell you if the polarity is reversed. There are both clips and O-rings.

The Moto Power unit operates at 0.8 amps, so it’s not the fastest charger. But speed is not critical to a good battery maintainer. There is automatic desulfation, which prevents the formation of crystals of lead sulfate. There’s debate about whether that’s necessary. Regardless, it comes with a two-year warranty.

Noco Genius Battery Maintainer
$30

Noco Genius works with six or 12 volts. There is an integrated thermal sensor to check the temperature. The unit varies the current to avoid over-charging in hot climates or under-charging in cold weather.

The company says it can fight battery sulfation and acid stratification.

Optima Chargers Digital 400 Performance Battery Maintainer and Charger
Around $90

Optima Chargers Digital 400 Performance Maintainer is another high-end unit, boasting a hybrid LED battery-charging gauge with an LCD screen and quick-set battery type selection. It’s one of the faster units, operating at a maximum of four amps.

Optima is a brand-name battery maker. The manufacturer’s claim: “It recovers discharged batteries that others cannot.” That includes deeply discharged units. It comes with a dual-purpose stand and wall-organizer bracket.

Schumacher SC1299
$20 to $25

Schumacher SC1299 is a relatively slow 0.8-amp charger. That’s plenty for maintenance work, especially if you’re not in a rush to bring a dead battery back to life.

This unit won’t work if clamps are reversed. It can be employed for standard, AGM, and gel batteries. An LED indicates charging status—pulsing green means it has power, solid green shows charging, and solid red—beware, reversed clamps!

Also read: Car Memory Saver: The Tool You Need When Changing Your Car’s Battery

See Automatic Battery Charger for sale on eBay.