Re: Which Battery to Buy?
 

Correlation comes in many flavors. What sort of correlation did you have in mind?

Perhaps a statistical correlation between internal resistance (as measured by Battery Beak) vs amp hours (as measured by CBA at various loads) ?

Re: Which Battery to Buy?
 

I'd like to know if you can detect bad cells with this correlation as well. We've seen individual cells drop out after 30 minutes and the battery continued to discharge for another 30 afterwards (I think I still have the plots for this one)

Re: Which Battery to Buy?
 

For batteries with bad cells, the jury is still out. There is some anecdotal evidence that bad cells will not necessarily be detected by the BB internal resistance test.

That's why some teams test their batteries at the beginning of each season with CBA (to weed out the bad ones), and use BB at competitions to check the bot's battery before rolling the bot out to the field.

Re: Which Battery to Buy?
 

Based on experience from you and others here, the theory seems to be:

1. Any battery that fails the battery beak or a high current load of 100+ amps should correlate to reduced capacity.
2. Vice versa, a battery failing capacity may or may not correlate to a fail based on a battery beak or a high amp test.

Some examples that demonstrate these situations would be helpful to the community.

Re: Which Battery to Buy?
 

I was wondering what CBA bomb squad purchased? It would be great if you could find a link.

Re: Which Battery to Buy?
 

Lately we've had our older Genesis batteries from 2012 expanding and become very hot. We will never get these again.
The MK's that we've used previously and this year is what we will stick to from here on out.

Re: Which Battery to Buy?
 

Under what conditions was this occurring? During use? During charging?

Re: Which Battery to Buy?
 

This was during charging.
We would come the next day and the whole place would stink up.

With the MK's that we used in the past, we could have them on the charger continuously for years and never had issues with them.
They obviously didnt hold their charge as before, but other than that, no issues.
I should have taken a picture before we disposed of a few more this past weekend.

Re: Which Battery to Buy?
 

Have these batteries been abused at some point? This is very unusual since Enersys is one of the premium battery brands. You may want to check your charging current.

At work, we have used tons (literally) of the 7AH version of the Genesis battery, every week, for at least the last 10-12 years without seeing this symptom. They are used in UPS and are on trickle charge continuously until there is a power outage. The UPS' they go into are used to run hospitals (yes, the whole building), data centers, air traffic control systems and other critical infrastructure. There is even one at the observatory on Maui. We do recommend that our customers replace the batteries every 3 years since they start losing capacity. Our Field Service people do run into symptoms like this when customers replace the batteries with cheaper brands.

Re: Which Battery to Buy?
 

Our batteries havent been abused at all. Since we started doing FRC, we have charged them in the same way and fashion. We never experienced any battery issues (other than losing capacity) until this year with our 2012 Enersys stock throughtout the past several months. Earlier this week, we just decided to dispose of them all to prevent more of them having similar symptoms. We normally used the MK ones over the years, but in 2012 went with Enersys instead.
Strange.:confused:

Re: Which Battery to Buy?
 

You might want to check your charger out. Cell swelling is one sign of overcharging, although it is not unique to it.

Re: Which Battery to Buy?
 

Counterfeits are always possible.

Re: Which Battery to Buy?
 

My wife and I are into cars...we have eight of them registered/insured right now. With a fleet this size, I get to deal with battery maintenance as a regular thing. Years ago, I decided the solution is to replace batteries every five years, and use the least expensive batteries I can find. It's worked great, I haven't had any battery or charging system failures for a long long time.

With the sealed batteries that we use in robotics, the same thing applies, but I would put the expected lifetime (for our team) closer to three years...mainly because of iffy battery maintenance. I can't seem to get anyone else to care about them, and I've given up trying. I (and the teachers) don't have access to the school during summer, and I'm not there often in the fall.

Re: Which Battery to Buy?
 

Strange indeed. Having met your team, I would expect that they are not doing wild and crazy things. You may have had a bad batch. It happens to even the best manufacturers. Once they swell, they can leak acid so if you have had several go bad, it is best to dispose of them all.

That is also a possibility. We've been victims of counterfeit parts here at work several times.

Re: Which Battery to Buy?
 

Me too.

I've got a large fleet of vehicles and for some of them I've just gone to battery sharing since a number of them do not see any use in the winter and some like my dump truck only gets used a couple of times per year. Personally I go with Costco batteries for the majority of my vehicles, if they have the appropriate size. The wife's primary drivers always get top of the line batteries as does my daughter's car. I also replace those and my primary driver at about 5 years too.

I tried for a number of years to school everyone on the proper care of the FRC batteries to maximize the lifespan. Yet despite the fact that we have the batteries numbered people just grab a random battery, "because we are only testing". They then proceed to drain it completely and often don't put it on the charger.

Just last week they were doing some testing on last year's robot which has been retrofitted with this year's control system. They were complaining that it was acting funny. I walked over and knew immediately by the sound the compressor was making that the battery was seriously low. I asked what the voltage on the dashboard was and with everything off it was showing 9.5 volts. I just had to walk away particularly when that dead battery was just set aside and not put on the charger.