Recommendations for 6-amp battery chargers


We have been having some issues with dead batteries that were being deep discharged.

What are your recommendations for a battery charger that can give us an accurate green led when the battery is fully charged and also have the ability to repair potentially bad batteries?


First off, are your current battery chargers showing a green light to say that the batteries are charged?

Second, how fast do the batteries run down?

Third (optional), have you exposed your batteries to higher than normal heat recently?

It sounds like you are getting a surface charge on your batteries. They act fully charged, but are not. If the answer to at least the first two questions is yes, you may need to mark the batteries in question as unfit for competition, then get them fully tested. (If the answer to the third question is also yes, don’t bother with the testing; of course, this is at the team’s option.)

This happened to us once under the circumstances above.

Third question: Have you left your deeply discharged batteries sitting around for hours at a time?

The primary enemy of lead acid batteries is sulfation. When you discharge a lead acid battery, the lead turns to lead sulfate. If left to sit long enough, the lead sulfate will crystallize into a very hard form that just won’t dissolve again. Thus you end up losing reactants, and you battery holds less charge. Any battery below 11V is in actual danger of sulfation. The more dead the battery, the faster the sulfation. Plus, batteries discharge themselves over time. If you just leave them sitting about over the summer, they’ll discharge and sulfate. The obvious solution is a well planned strategy for maintaining your batteries.

High heat is a seperate problem. That could potentially boil off some of the electrolyte and dry out the battery.

Some practices here and here should work simmilarly for robot battery.

If you want a good battery charger that will take a possibly dying battery and revive it some look here and here. You shouldnt have too hard of a time getting a desulfator charger from an automotive store near by you. The batteries will take longer to charge initially but if they’re not totally dead they will regain much of their usefulness. Most of the newer computerized chargers, like the ones in the kit and simmilar by other companies will give a proper voltage, but they cant tell if the batteries’ plates are good or not.

-Mike Aalderink

The batteries we use have a very finite life. Under normal conditions this is about 400 charge/discharge cycles. Most teams do not use the batteries in normal conditions. A robot runs very high discharge rates and rapid charging repeatedly for several days during competitions. Sulphation is not as big a problem with gelcells as with standard lead acid batteries but it does occur. I don’t think that is the case with your batteries. If you drain a battery in one match consider that the life of the battery has been cut in half. We have been finding that several batteries we use, are starting to deteriorate on a cell by cell basis. We test the suspect batteries using a Mountain Radio computerized battery charger. It shows that one cell (2volts) may have significantly less capacity than the other cells in the battery. I suspect that the heavy use has damaged plate connections within the cell. Some of the batteries show about a 4 amp hour rating on one or two cells while the rest of the cells remain near the 18 amp hour capacity. We have had one new battery, out of the box, show this problem. If you run you batteries for a few minutes and then check the voltage and the reading is a multiple of 2 volts below 12 volts (with no load) suspect a bad cell and not the battery as a whole.
There is no reasonably priced charger that will fix the sulphation problem and nothing can fix the defective cell problem.

Al, is this the battery analyzer you use?

West Mountain Radio is also a good source for crimpers to attach the 45A miniature Anderson-style connectors that we use with all of our motors; these are shown attached to the analyzer in the above link.

Yes that is the one, Rich. We can get it to discharge at about 7 amps without tripping the software or hardware into fault. It gives a nice plot of terminal voltage over time and calculates the amp hour capacity. It saves the data and will even print labels for the battery you test. A nice small package with fan and USB cable.

Thanks, Al.

The price seems OK, too: about $100. Much better than trying to duplicate this capability with a lab set-up, even if you have the equipment.

I just ordered one.

We have a West Mountain Radio CBA II that we use to test all of our team batteries as well. It can sink 100 Watts so the max test you can run is about 7.5 Amps. It is a really handy unit and I highly recommend one for every team. I test all of our batteries throughly before and after comp and rank them from strongest to weakest with big red numbers so you can quickly grab the next strongest battery that is fully charged in the pit. I haven’t completed the post comp tests yet for this year but will post some results here if there is any interest. I have tests for 9 batteries from 2003 to 2006. Surprisingly, the new 2006 batteries are we got in this years KoP are NOT our strongest batteries. One of our 2005 and one of our 2003 batteries have consistently tested stronger than one of our new 2006 batteries. Last year one of the 2005 battery was junk right from the start. If teams assume that the new batteries they receive are stronger than older batteries from previous years they may be making a false assumption. In fact, it is a bad idea to assume the batteries you receive with the KoP are even any good. The CBA II is a really great tool to help diagnose the strengths and weaknesses of batteries. Another cool tool I use is a Medusa Research Power Analyzer. You can even connect it in-line between the battery being tested and the CBA II to double check the measurements from the CBA II. I have an older Power Analyzer Plus and the new Pro. The neat thing about the Pro is you can have it control your ESC (read Victor). It is a great tool to test current drain and debug stuff right on the robot. One other nifty little test device that every team should have on their test bench is a FMA Direct Servo Lab which you can get from Tower Hobbies for about $35. It is a really handy device for testing Victors and putting in-line between the RC and a Victor or Servo and to read and/or control PWM devices.

As to the original question of the post, we use the chargers that come in the KoP and some Schumacher 2/4/6 Amp Smart Chargers that you can get at Wal-Mart for about $25-$30 (IIRC). They are identical to this SC-600A model but sold at Wal-Mart for less with a WM-600A model number.

Thanks for the help.

The problem we have with the KOP chargers is that even brand new batteries, when charged for days, will never show a completely green LED that doesn’t flash. We purchased 6 new batteries, and 3 new chargers, and let them all properly charge for the reccomended 14+ hours. The LED was green, but it flashed yellow every 10 seconds or so.

To me, this is a bad thing for students who want to quickly grab a battery to put in the robot. They are sitting there looking for the light to stop flashing, when in reality, it never will! Ive seen them more than a few times counting the time between flashes, and then grabbing the one that flashes the least! Granted, you would think there is some logic in doing that, but it never seems to work.

What we want is a charger that gives as an accurate status of the batteries charge level. I know some of the more expensive 3 stage chargers have this ability? I think it would be much prefered.

I also am going to try and convince to team to purchase one of those Computerized battery analyzers. That would help us seperate good and bad batteries much more easily.

Thanks again!

Depending upon your wallet, try the interacter charger available at
it is also available as a 5 bank unit. This is the unit we use.
It is a true three stage charger, with a green light that does not
lie and a yellow light that indicates greater than 80% charge status.
The five bank unit will keep an entire alliance topped
off for a trip through the finals.

Anyone have any recommendations to these chargers?:
(Buspro 600)

and the…
(INTERACTER Battery Charger)


I agree with Tavis. We have been spending too much time playing with battery chargers and deciding if batteries are charged. We even look through the LED from the top to better see the color of green and if the LED has quit blinking.

Here is what we are doing to make life easier: we bought one, so far, a Shumacher Speed Charger, model # WM-600A. I bought it at Walmart before we left for Inglewood last year. The cost was $25. The charger meets the requirements for the competition and has % charged indicators from 25 to 100%. The charger has three red bars and graduates to one green bar when charging is complete. Best of all no guess work. In addition, we have converted the alligator clips to an Anderson connector. No more wondering if we have a good connection from the charger to the battery, and no more arc welding in the pits.

One down side to the charger is it defaults to 2 amps when first connecting to a battery. Not to worry: two pushes of the button and you go from 2, 4, to 6 amps.