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Model # BM3B

Internet # 202710992

Store SKU # 273222

120-Volt Battery Maintainer

This item has been discontinued.
The Home Depot no longer carries this specific product.

$22.02 /each




Model # BM3B

Internet # 202710992

Store SKU # 273222

The BLACK and DECKER BM3B is ideal for keeping your 6-Volt or 12-Volt battery fully charged when not in use. Simply plug the maintainer into any AC outlet and connect to your battery in any one three ways: Battery clips 12-Volt Dc accessory plug or the battery terminal rings. The BM3B will do the rest of the work, monitoring your battery with the Automatic micro processor, so that you can never over charge the battery.

  • For use with both 6-volt and 12-volt batteries
  • Automatic microprocessor battery monitoring
  • Reverse connection warning and ready indicator
  • 3 ways to connect battery clips, 12-volt accessory plug, and battery ring terminals
  • Home Depot Protection Plan:

    Home Depot Protection Plan


Product Depth (in.) 
Product Height (in.) 
Product Width (in.) 
Amperage (amps) 
Automatic shutoff 
Battery Test Function 
Battery tester included 
Charger type 
AC or DC 
Cooling fan 
Cord Length (ft.) 
Engine start function 
Product Weight (lb.) 
1.35 lb 
Reverse Polarity Protection 
Voltage Output (volts) 
120 V 
Warranty / Certifications
Certifications and Listings 
1-UL Listed,ETL Listed 
Manufacturer Warranty 


Rated 4.8 out of 5 by 40 reviewers.
Rated 5.0 out of 5.0 by Terrific unit I found myself in a situation where I had to store my motorcycles remotely, while I moved cities. At home I used a an ultimate unite that I swapped between 3 bikes, but with a move I had to store the bikes a 2 hr drive away for several months and I had to find an alternative, reasonable cost solution. The ultimate is a great device also but way more costly. I decided to order two of these B&D units as I have always been happy with their products. I researched the background and figured if B&D bought the company that designed these they must be OK. I hooked up two of my bikes with these units and left them for 5 months alone in storage hoping I would not need to buy new batteries when I got the bikes out. When I got back, the green LEDs were illuminated on both units. Turned the keys and both bikes started up like champs. Batteries were strong cranking and kept fully charged. I have since moved the bikes to the new house and these units are on them constantly while we endure winter in the east. really really satisfied with this product. At 20 bucks each I already exceeded the value from them in saving me over $200 cost in new bike batteries. They saved me in this storage and now are holding me through winter. Enough said!! December 6, 2013
Rated 5.0 out of 5.0 by DOES THE TRICK, OR SHOULD I SAY TRICKLE...... Have a car that is sitting in garage now and the battery is slowing being tapped , so I hooked this up and in about 24 hrs. , brought it right back to snuff...I followed the next week and it only took about 4 hrs. to top it,,,,,,.I do agree with others the volt. selector switch is too easily moved from 6-12 volts....but just be careful or tape over it....It's better to slow charge a battery than rapid with higher amps in the long run.....and this is about 1.2 amps..vs.. 4-10 amp units.... December 30, 2014
Rated 5.0 out of 5.0 by meet or exceed my expectation I got this from Home Depot with the best price on market, June-2012. Good luck looking for equal or better price elsewhere. It can be found in hardware department where B&K are display. You may want to call first before heading there, not much left. It supports three style of connections, battery terminal, jumbo alligator clips and accessory outlet connections. Me and specially my wife likes the latter. I test this charger with car battery about 85% full, meter reads 1.5 amp. and reducing over time as the battery is taking charge, during which I recorded 14.7 Volt. This does not imply charge current can't reach factory specification limit, just the nature of current normally reducing approaching full charge. It determined the battery have reached full charge then mode switch to maintenance holding a voltage measured at 13.6~13.7 Volts which is also the open circuit output voltage. The case temperature well into normal charge was noticeably warm to touch but not hot enough to cause my concern on smoke hazard. The case temperature drop next to ambient about half hour into maintenance mode. I inspect the guts have found a switching regulator, the kind of design we normally find in laptop ac adapter power supply, all have efficiency of 80% or higher. In addition to that is a relay switch toggling between two charging modes. Pulsing green inidcator in normal charge and steady in maintenance and dc open circuit. I am very pleased of what I find inside and out (accessories) for the price I paid at Home Depot. If I buy the these accessories harness separate would cost me more than I paid for this package. Hope this helps. July 6, 2012
Rated 5.0 out of 5.0 by Piece of mind having my battery maintainer Bought the 6/12 volt battery maintainer so I would not have to worry if there was enough charge on my battery to start my "classic" car. My car sits in a separate garage and I don't start it every week, sometimes not for a few weeks and at times the car has a hard time starting and I have to hook up the charger or jump it. Now with the battery maintainer, I never have to worry if there is enough juice to start my 1937 Dodge!!!! I wish I would have done it years ago. December 10, 2014
Rated 5.0 out of 5.0 by DC Residential Lighting System Our home has built-in 12vdc LED lighting in most rooms that operates from a large, central deep cycle battery. It can operate our house for about a week before needing to be topped off (typically @ 70% charge). The battery was rotated with another one in our solar powered workshop and recharged away from the house. A minor hassle - but worth it for clean, bright Off-Grid illumination. Attaching this BM3B trickle charger to the central battery has made it in effect a Uninterrupted Power Supply - keeping the voltage close to a healthy full charge at all times and eliminating the weekly switch-out. And when the grid goes down for an extended period (as happens in our rural area a couple of times a year) we still have the solar recharge option. It installed very easily. Took a few hours to top-off the deep cycle - but went into float mode overnight and kicks back into trickle charge mode for a few hours after a night of using the lights around the house. Its case gets slightly warm when charging. Expected. Mounting screw holes are very useful in our application. I agree about the 6v/12v switch feeling a little cheap - it needs to be more "clicky" to instill confidence that it won't easily/accidentally be knocked into the wrong voltage setting. Only thing yet to be proven is it's long-term serviceability. Here's hoping - it's a very simple and elegant solution! February 15, 2014
Rated 5.0 out of 5.0 by Best auto trickle charger I've seen! Couldn't be better....just plug in, hook up and it does the rest, as advertised. December 10, 2014
Rated 4.0 out of 5.0 by Battery Trickel Charger I use this charger on my lawn tractor to keep the battery fully charged, especially in the winter. It works well for me, as it is small, portable and has long enough leads to fit from under my carport to the tractor. Best of all, the price is very affordable and it is very easy to use. Mr. T El Paso, TX January 20, 2015
Rated 5.0 out of 5.0 by As advertised I got what I wanted, at a good price. It will maintain a battery, although it may take a long time to charge even a small heavily discharged battery. December 6, 2011
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