What I learned about battery chargers

Authors note: I already spent a lot of time and about $30 on this post. If you think I'm gonna spend one minute proofreading it, you're crazy. Now read it, because I would like to hear your input, and maybe you can point out the spelling and grammar errors.
I learned very little, but I think I have an interesting story here.
A few days back I saw this post at The Feral Irishman about the Battery Tender brand battery maintainer.  It got me thinking about a few things that I have wondered about for years, but never spent the effort to find the answers.  Well, for some reason, reading that post finally gave me the motivation to try to find some answers.

The first I ever heard of the Battery Tender was about ten or twelve years ago while watching those car repair/customization shows on cable TV.  I always wondered why this Battery Tender was any better than a regular old trickle charger.  

You might wonder why I even bother to care about such things.  Well here’s why.  About 16 years ago, when I moved into my current home, I wanted a radio for the kitchen.  Now that was a problem because virtually all radios for the home at that time sucked, and for the most part, they still do today.  Most of them still have old school analog tuning, no station presets, staticy AM reception that is susceptible to interference from the use of other electric appliances, aren't loud enough, and have terrible sound quality.  Now they do make some units that don't have these problems, but they are either very big (home stereo receivers) or very expensive. (Bose wave radio)

I wanted something that was free of all these problems, and fortunately, I had the solution - a car stereo, in my house.  Think that’s crazy?  I challenge you to come up with anything else that has all the features of a car stereo and comes in such a compact size for even twice the price. Remember, I went through all this well before the age of ipods and smartphones, and since I’m one of those dinosaurs that still doesn’t have a smartphone, this option remains perfect for me.  The nice thing about it is that it doesn’t take up much space, and since I mounted it inside of a cabinet, you can’t even notice that it is there.

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At first I thought I could hook this up to a twelve volt DC power transformer,

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but that caused static on the AM band, so I was forced to use a twelve volt battery.  (I looked on Youtube, and noticed that some guys are using a PSU robbed out of an old computer for this purpose, but for a number of reasons, I felt the battery was a better way to go, and I’m not going to go off on that tangent right now.)  The garage is on the other side of our kitchen wall, so I just drilled a small hole in the wall to allow the power and antenna wires to pass through.  The battery and antenna are located in the garage. 

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I often thought of mounting the antenna outside, but the reception was good enough with it in the garage, so that’s where I left it.  The speakers are located on top of the kitchen cabinets.  They’re so close to the ceiling, that no one notices that they are there.  The system worked so well for me, a couple of years later, I installed a similar one in my wife’s hair salon.

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Now, I needed some way to keep the battery charged and this is where my question about the Battery Tender comes in.  Would the Battery Tender be better for this application than regular old trickle charger?  The answer is: Maybe, but not a whole lot.  The advantage of the Battery Tender is that it is a float charger, which means that it does not constantly charge the battery so it doesn’t boil all the water out of it, however, I just checked the battery in the picture above for the first time in 16 years and the battery fluid level was just a little low.  (About a shot glass low in each cell.)

Here’s the chargers that I have been using for over a decade, still with the original batteries.

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Here’s how the manufacturer describes their current model which appears to be similar to the ones I have...

The Schumacher SE-1-12S Fully Automatic 1.5-amp Onboard Battery Charger is an AC powered automatic trickle charger / maintainer for use with 12 volt lead-acid batteries. The unit features an automatic charge cycling process that allows charging to turn on and off automatically as is necessary, and its "onboard" design and included hardware makes for easy, convenient mounting adjacent to batteries both inside and away from vehicles.

...so I’m thinking, how much better could the Battery Tender possibly be? What 's the difference between this and a "float charger"?
Here’s what the Battery tender folks have to say.
I set up these home car stereo systems before I ever even heard of the Battery Tender, so didn’t think twice about using the Schumacher units.  My memory was that the Schumacher trickle chargers were much cheaper than the Battery Tender, but I just checked out the prices of each, and comparable units appear to be about the same price - right around $25.  

Now, how much energy do they use?  After all, if you buy one of these units, you are probably going to hook it up to a battery, walk away, leave it on 24/7, and not look at again for a few months.  Not the kind of thing you want to do with something that consumes a lot of electricity.  Well, it's kind of tough to answer since these units do not charge continuously, even if they are constantly plugged in.

If they were 100 percent efficient and they were charging at all times, they would be using about 180 watts at any given time. (1.5A X 120V = 180W)  In this case they would cost about $186 per year to operate.  (180W/1000 X 8760hrs/year X .12/kWh)  However, they are not 100% efficient and they do not charge 100% of the time. For determining the energy useage for something that runs intermittently (like a battery maintainer), without you knowing how long or how often it is actually running, doing this type of calculation is just about useless, so I bought this thing:


The problem with this thing is you must use it for several days to get a realistic idea of how much energy an appliance that runs intermittently uses, and that’s not going to do any of us any good right now.

So after all this, what’s the bottom line?  What’s better a Battery Tender or the Schumacher trickle charger?  Is there really any appreciable difference?  After all this, I can honestly say, “I don’t know”. but since they are about the same price, I think the Battery Tender might be better.

What do you think? Should I switch to the Battery Tender? Is my whole car stereo in the home idea stupid or dangerous? I'd love to hear any of your thoughts on the subject.

I'm not done talking about battery chargers yet. Look for an update once I get some usable data from this Kill A Watt power monitor thing and look for a more automotive specific post about battery chargers coming soon on "Right Side of the Road".
UPDATE!  UPDATE! - After monitoring the power consumption of my trickle charger for about 10 hours, the Kill A Watt meter says that it's energy use varies between 5 and 9 watts at any given time and has a projected energy cost of $7.88 per year.  How much cheaper could the Battery Tender be to operate?  It's probably still too soon to get a truly accurate reading, and the possibility exists that I am using/reading the Kill A Watt meter incorrectly.  I will be more confident about my results after I use it more and thoroughly read the directions, but that's what I have so far.   


  1. Hmmmm.

    Well...you're taking readily available AC, converting it to DC, and back to AC again. And, if the object is superior sound, your car stereos, even the best ones, will never rival the in situ home systems built by the serious audiophiles. There is a minor electrical fire hazard posed by the battery I suppose, but the chargers are thermally and electrically protected and safe guarded. The insurance people might not like it.

    In spite of all that it is a darn cool thought experiment and a worthy project for some enlightening tinkering. Additional sport can be had in scrounging and fabbing your own parts!

    I suppose it would be cheating to go to something like the solar powered battery set ups that run the SCADA systems in remote well sites? Probably a few more $$$ too...

    Batteries are BFM to me (Black Fuggin Magic). I know that some chargers 'balance charge' the batteries so that all the internal cells of the battery carry the same voltage and thus prolong the battery life significantly. Others will discharge the battery to optimal nominal voltage levels for long term storage. But most of that is on the leading edge of battery technology...you are dealing with old school stuff here so I dunno if that comes into play or not.

    Is high tech (and costlier components) allowable in your project Neil? I would like to see how you make out with all this. Good luck!

    1. This is a 15 year old project and I don't have any complaints so far. As far as sound quality is concerned, you are absolutely right. I can remember years ago, comparing car stereos to quality home stereos. The home stereo systems had much better sound quality than the car stereos.(distortion levels, etc.) However compared to a typical home radio, the sound quality of the car stereo is far superior. Because of their physical size, a home stereo system was out of the question and systems like the Bose Wave radio were ridiculously expensive for a kitchen radio. Nothing I could find even came close to the sound quality of a car stereo for the price, and nothing else had as many features. I also liked the fact that my car/home stereo still worked during power outages because of the battery.

      P.S. Check out the update on this post.

  2. Couple of points:

    Your math is off. You have 1.5 amps at 12 v not 120.

    neither charger runs all the time, they are maintainers as well. So they charge, pause, check, charge again (or wait and then check again). actual charge time is something between 5% and 70%.

    The SCHUMACHER unit (as shown in the picture) is also a battery tender, not just a charger. It maintains in a similar manner to the Battery Tender. These are not just tricklechargers.

    1. "Your math is off. You have 1.5 amps at 12 v not 120." I know that all this is confusing, I was talking about the INPUT not the OUTPUT.Yes, the output is indeed 12V, but the input is 120V. In order to get a true estimation of power usage without having to deal with inefficiencies, you must use the input to determine power consumption.

      The next thing you said, "neither charger runs all the time, they are maintainers as well. So they charge, pause, check, charge again (or wait and then check again). actual charge time is something between 5% and 70%" is indeed correct and was confirmed by my use of the Kill A Watt monitor.

      You seem to be quite knowledgeable about this subject, so let me ask you these questions: 1) Is the Schumcher unit just as good as a comparable Battery Tender? 2) Is the Schumacher unit a float charger? 3) If not what does a float charger do that the Schumacher unit does not do?

    2. Yeah, but the 1.5 amp spec you used is the output, not the input. if you measure the input amps, you'll find that they are more like 0.18 amps. The unit puts out 18 watts, not 180. There is a small inefficiency but again, it is 18watts.,

      There isn't much difference between the Schumacher "maintainer" and the Battery Tender....They both charge, then check voltage (IIRC, the Battery Tender actually discharges fora fraction of a second while checking voltage) and they use a different algorithm for when and how much to charge. Both will maintain a battery without sulphating the battery or running it dry quickly.

      A "Float" charger maintains a small voltage across the battery at all times, with the resultant constant current flow. this aids in suphation of the plates (current flows in only one direction through the electrolyte) and also slightly heats the electrolyte, leading to higher evaporation rates, causing the battery to eventually go dry.

      Ideally, the float charger *just* compensates for the natural discharge rate of the battery, but in practice it is usually a higher rate of charge. The maintainers and tenders test before charging, greatly reducing the sulphation rate and the evaporation rate, They charge only when needed, greatly extending the battery life and making sure that they have a charge when needed. Often, people who have only a float charger can use a timer to get a similar result, turning the charger on and off several times a day to reduce suphation and evaporation and still get a decent charge. .

    3. Thank you. You cleared up some things that I wondered about for about 15 years. Back when they first introduced the Battery Tender, they talked about it like it was something revolutionary, and I always wondered what it did that the Schumacher unit didn't do. I guess it was mostly just sales hype.

  3. I thought that I was the only crazy person out there that used car audio stuff in the house. None of the radios that I had at the time got good reception in the basement where I spent way too much time. I mounted my 1974 vintage Kraco 8-track quad matrix and a Delco am/fm radio on the beam above my work/loading bench. These were powered by an old car battery that I would hook to a 1 amp charger overnight about every month or so just in case the juice was getting low. I never could tell since I didn't have a battery tester. The radio reception was fine with just an old car antenna stapled to the side of the bench. And you are right about how nice it is to be able to use that stuff when the power is out.

    1. For the money, nothing even comes close to a car stereo for sound quality and features. The things I like most is the compact size, electronic tuning and station presets. You have to buy a very expensive home system to get those.

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