We have been testing our battery stock with the West Mountain Radio CBA testing device. Attached is an excellent example of a discharge curve for a bad battery with two faulty cells. One can clearly see the 2 volt drop from each cell as the battery discharges. This one is already on its way to the recycler.
That is a bad battery. It sure would seem that there is something going on internally as well. I have seen the two volt drops before, but I have not experienced the rise that is shown. It would seem that maybe some internal heating is shorting something then opening again. Is this battery less weight than a new one? I often wonder on a battery with curves like this, that maybe some venting has occurred in the past and the plates are not fully covered by electrolyte. Is it warm as you run the test?
It is an old Exide battery from 2006. I had a student running the test and I just saw the report when he was finished. Would you like the battery? If so I may still be able to recover it and send it to you. We will check the vents to try to determine if any are open or damaged. There was no evidence of obvious electrolyte leakage.
I have a seen enough of these, the report was a great example. Please recycle it. As much as I would love to open it up and examine the innards, I don’t have the facility for handling the parts inside.
Thanks for the offer.
Would you ind if I copied the report and maybe use it in my presentations?
Again more reason for teams to invest in a load tester, available in many auto parts stores or on-line. We suffered 2 bad batteries in 2008 that costed us several matches at Atlanta - never again!! When charging and tested with a standard voltmeter, we thought all was good. But when the batteries were put under load during a match, the voltage would drop to 6 or 8 Volts.
I also have a sneaky suspicion that this year, batteries will take a beating with all the up and down over the bump and hanging / falling. Also teams maybe tempted to lay the battery down to lower the CG, but when it is on it’s side, it is more prone to damage the internal plates. Keeping the battery vertical when the bot goes up and over the bumps, along with some cushioning, may be help batteries survive.
We have the same tester and have used it to test our battery collection. We found two that had the same cell pattern shown, they are scheduled to be recycled. (They are also from 2006). We’ve ranked the batteries in order of performance, so we have 5 good ones for matches and three for general testing / shop use.
I also tested our VEX battery supply (with 9 teams we have a lot of them) and was able to pull out some ones that were not 100%. I’ll be bringing the tester to Fingerlakes and Drexel and if teams can give them up for 30 minutes at a time I can test batteries for teams.
The tester has been very helpful and I think has paid for itself.
As a reminder to those who are lurking here, the batteries have a finite life. Under normal conditions, that would be 400 charge/discharge cycles. Under our use, I would expect that to decrease by as much as 25%. It is not unusual for a 2006 battery to have gone through so much that it is now ready to retire.