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Originally Posted by dez250
Kara this sounds very interesting and I would go on a limb and say it is not the batteries themselves but how your team may be treating them. If you have gone through seven batteries in two years, I would look mainly at your chargers and how students are handling them. While it may not seem evident, handling the batteries by the cables or lugs directly can cause major damage, along with the obvious of dropping a battery will damage it. The plates that create the chemical reaction in them can shift or even pull out partially through mishandling.
Also what type of chargers are you using, and what connectors are on them? If you are not using a "smart" charger at the right current rating, you can be over or undercharging the batteries, thus again causing damage. Finally I would look at the connectors on the battery chargers, if they are alligator style clips, change the connector. The gator clips scratch the anderson connectors contacts and create an inefficient connection later on when in the robot. I would cut off the gator clips if present and swap them out for anderson half connectors, the same as used on the battery to make a solid connection.
As for failures with these batteries, if you see the battery dropping in 2 volt increments that is showing a failed single cell (per 2 volts) and means it is time to replace that battery.
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I'm sure that a lot of the issues WERE caused by improper treatment of the batteries. As much as we stress how important it is to not carry a battery by the cables, it inevitably happens occasionally when someone is in a hurry between matches. Some of the batteries that we retired and replaced this year were as old as 2007, and had suffered through four full seasons of use and abuse. I know that a few of them had indeed been incorrectly charged.
We do use the Anderson half connectors instead of the gator clips. I don't know offhand what kind of chargers we use. We replaced our age-old ones this year because we had the money, and the old chargers were going bad in one way or another. We also acquired a load tester during the fall, and have used it.
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Originally Posted by Mike Betts
We did the tests because the team thought that we had "bad" batteries. Several batteries had been marked as "bad" by the pit crew during a regional competition. That year, the game was "Aim High" and the requirements of the shooter mechanism, drive system, pneumatics pump, et cetera, was so great that the battery voltage would crash during a match.
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I believe that, though I don't think that it was the case for us this year. We had one battery that consistently died during matches. As none of the other ones gave us problems when fully charged, I'm inclined to think that the failures were not coincidences related to gameplay.
Thank you both for your advice. Next time I have a chance to talk to my mentors with the batteries next to us, I'll pass on the information.