MK Battery Problems

Anyone that watched the Finals at Buckeye probably wondered what happened to 1126 in the last match. They had the same problem we faced this year. A bad Battery. Our Rookies (424) lost a match in the semi-finals that we thought was a wiring problem. It wasn’t. As it turned out the wiring was fine it was a bad MK battery. We had 2 blow this year at competition and another 2 go down in the pre-season. I was a bit curious when we pulled the battery out of the robot & it gave a full voltage reading. We put it in a robot & tried to run, it drops down to a dead reading. When I was holding the battery I felt a warm spot about 2 inches wide that ran from bottom to top on one side. I talked with some of our electrical people I was told that it probably has a bad cell. We have checked out our chargers & they are not the problem. In the previous 7 years we have only had 1 bad battery out of dozens. (some do die over time)

What I want to know is, how many other teams have bad batteries? I would like to contact MK but I would love for some more Ammo before I do.

You are not the only team who has expeerienced this trouble this year. I invite all teams with battery problems to PM me with details please. I need to know the charger you were using for that battery prior to the defect. About how long it was in service (did you use it for practice and/or how many events), does it show any signs of being dropped (a ding in the side or a rounded corner) and how long does a normal battery last on your robot. Also is there any case deformation (swelling). Inspectors will also be interested in any failures you have at Champs. I will be inspecting and you should be able to find me on the pit floor if you have any problems you would like to show me then. Pictures are also helpful.

We have a battery that acts like that. It seems to charge fine, and seems to show a good voltage when not under load, but the voltage drops immediately when used.

We have a good idea of what went wrong with it. This particular battery once started to fall from a table, and was “saved” by someone catching it by the wires.

125 experienced the same thing in boston, there werwe 2 matches that i remember that we could not winch our catapult back b/c the battery was toasted, there is nothing more frustrating than that, espctially when the batt has been charting for over an hour!

During finals the drive team got a battery from Spare Parts, but it was defective on the field. There’s no telling though how it was treated beforehand.

One of our own MK batteries was bad in the finals as well. I’ll get more details from the pit crew about when good batteries go bad…
We will also be bench testing our failed battery this evening.

Mark, was the second battery from spare parts okay? Maybe there was a problem with the chargers at SBPLI. I saw the spare parts people charging the extra batteries troughout Saturday. Maybe the batteries were abused or mishandled at another regional.

-Joe (Elimnation Match Spare Battery Guy)

Actually team 25 has found that two of our new MK batteries from this season have failed (in Hawaii). They seem to be taking a charge but they rapidly lose it and are spent well before the round is over. We were attributing it to the fact that for the first time we have the battery mounted sideways and I was assuming that the cells were being jarred from robot impacts.

Normally we mount the cells upright and a battery lasts past a single season. We are ordering a few replacements for the Championships later this month.

If this is a “bad batch” of batteries I would like more info. We charge with the exact same type of chargers the kit has included for the last few years (prior to 2008)

WC :cool:

For those of you that measure the battery at full up no load and then it drops under load, what is the measured load terminal voltage? Does it fall by a multiple of 2 volts or does it go down to zero? Please give lot number/date code when you post.

Here is a little more info on our battery failures:

  1. The two batteries that failed were bought in 2007 and out of the same batch number. They did not come in the 2007 kit of parts.

  2. We only used these batteries in competition. (During the build season we use 2006 or earlier batteries.)

  3. We use previous years’ chargers to charge all batteries.

  4. We measured all of our 2007/2008 batteries’ impedance under load and found that they were mostly <10 mOhms ( which meets the current spec). The exceptions were the two that failed (about 5 Ohms) and one 2007 battery that was 12 mOhms. Testing was done on fully charged batteries. All of the batteries read >13V after charging and recovered to at least 12.5V after the load test (except one of the failed batteries which read 10.83V).

  5. We removed the plastic cover to expose each cell’s rubber cap. In the failed batteries these were “dimpled” indicating the battery was probably over heated at some point. The failed batteries also exhibited either a reddish residue or a trace of yellow liquid.

  6. The batteries show no indications of heavy impact, and none were dropped or handled by the cables. Also in both of our on-field failures there were no impacts that caused the failure.

  7. Our current robot does not draw significantly more current than any previous year’s electrical system, and battery voltage after a match is >12.5V. We can probably run two or three matches on a battery before seeing a performance drop, but we have not tried this with any of the 2007/2008 batteries.

One of the failures was a single cell failure as indicated by the voltage ( and the red discharge near one of the cells). The second failure is probably related to a loss of electrolyte.

At this point we are investigating the chargers, specifically, the charged voltage threshold and the trickle current over long periods. We are also (re)-implementing the battery tracking records ( time in, time out, match used etc.) as we were a little lax this year.

One more note:
In buying replacement batteries, the country of (manufacturing) origin has changed from Vietnam to China. We intend to characterize the new batteries this weekend.

We would appreciate any thoughts you have.

Mitch Milton
Team 1126 - Electrical sub-team

We have found that some of our batteries will not charge on the new Schumacher charger. It acts like it is starting the charge cycle them quickly goes to a red fault light. They charge just fine on the old ChargeXpress chargers.

1023 had a battery go bad this year. We charge our competition batteries on the old style chargers (2007 and earlier). We got down to the field and when the match started it read 10.8 volts not under load. It would drop to 5 under load. We attempted to recharge the battery and after the light was solid green we checked the voltage and it only read 10.7 volts. The battery was from 2007 and was used in 2007 build and 2 events, offseason, 2008 build and went bad in the middle of our first event. The battery will no longer hold a charge.

We had a battery act wierd like this on us this year and we marked it bad. I’m not sure when it came from… we aren’t really too good about cataloging batteries and all…

However, we didn’t catch in on the field, we caught it in the pit. I highly suggest teams own a Load Tester for their batteries… basically it’s a box of ceramic resistors with a built-in volt meter and a switch to apply/remove the load from the battery. We briefly test each of our batteries this way before they go to the field to make sure that they perform.

You should be able to get one at most auto parts stores.


I like to use a Vector Smart charger (AKA Power on board, AKA Craftsman). It gives a digital display of the charage rate, full charge and error messages if a battery fails to take a charge properly. It performs a three stage charge on the battery too. It identified a bad battery before we had an issue with it. The 2/4/6amp charger is also about the same price as the Speed Charger that comes in the KoP.

Just to keep things interesting, I’ll mention that we discovered that the Andersen connectors this year are made differently from past years, and that we could get the power to the robot to go on and off by merely wiggling the Andersen connector with the new batteries, but it would stay working with the old batteries (which have the old connectors).

Two of our batteries have issues similar to this.
We put the battery in the robot, switched it on, and nothing happened. The robot didn’t go on at all. We disconnected the Anderson connector and connected a different battery without actually moving the first one, switched it on and it was fine.
I think it was the battery, but after reading the thread I now suspect the Anderson connector as well. It has happened to us only a few times and each time, we haven’t done a thorough investigation of the problem.
I believe we have a mix of new and old Anderson connectors on the batteries (we taken them off old, dead ones).

The spec is 11mOhm nominal so I wouldn’t be too worried even up to 15 or 20 mOhm. However 5 ohms is way too high. I know the construction of this battery does make it possible to damage the terminal inside the red/black coating at each terminal. Picking up by the wire is a guaranteed failure.

Just to reiterate, team 125 had 2 bad batteries go down on us at the boston regional.

One was from 2007 KOP the other from 2008 KOP. Other than that I dont have the exact details from them, however when put under load (with a load tester) we got a reading around 9 V for both of them.

Brandon, when you use the load tester on an “in working order” battery, what is the “regular” reading you would get?

Our 2 batteries from the 2007 KOP act like they have take a charge then when you put them on the robot the voltage immediately drops. I haven’t load tested them, but we just don’t use them now. They went dead while we were using them on our 2007 bot to practice in the fall. They’ve been charged on both a NAPA charger and the new Schumaker.

To test the theory of a bad batch of batteries, here is the lot number for the bad batteries that SparX had.

Lot Number: 061009D