Bulging battery on both broad sides: Why?

One of last year’s batteries is bulging on both of the broad sides. (I have bagged it in three garbage bags and put it in a plastic box until I can recycle it). Both the battery charger and battery have been successfully used for these two seasons. We plugged the cart with the chargers in on Saturday evening when we got home from our first competition, and just discovered it today (Thursday). It was flat on Sunday.
Has anyone else had this happen?
This is our first encounter with “the bulge” and look forward to experience providing insights. Thank you.

It’s likely due to overcharging or short circuiting. I would stop using the charger and check any other batteries that may have been on the suspect charger.

+1 to this.

  • Sealed lead acid batteries go bad in 3-5 years and should be recycled at EOL.

  • A bad charger or charging at greater than 2 amps can cause bulging issues as well.

  • Extreme cold or heat can also age the battery faster.

  • If the battery starts to leak, use baking soda to clean the mess.

  • This battery should be recycled and not used for robot power ASAP.

Lead acid batteries evolve hydrogen gas when overcharged. There are vents that should let this gas out, but it sounds like the ones in your battery are jammed or broken. Definitely quarantine the charger that was last used on this battery and thoroughly check it before using it again.

I assume you mean for FRC use (or should I say abuse).

Well-taken-care-of sealed lead-acid batteries in automotive application typically last 10 years or more.

At least that’s been my experience in five decades of driving and auto ownership and maintenance.

Thank you all for your quick reply and great insights.
A follow-up. Has anyone else ever had their FRC bot batteries bulge on the sides? If so, were you able to track down its cause?
Thank you, again.

Is there any possibility it could have frozen?

Good question. No, we came right from the event, put it in my van and put it right back into the school.
I don’t see any bent case on the bottom. I know there were some hard hits during the meet, but this would be the first time in four years this has happened, and in those past years we have hit things a lot harder in practice than in these past meets. Just wondering if anyone else had this. It was last year’s KOP.

Hard hits and physical damage can cause off-gassing from batteries (maybe from a broken plate and internal short?). Our only battery issue was from this in 2013, but the vents did their job in our situation.

What constitutes well-taken care of, besides not running it down (I know automotive batteries dislike deep cycles) and checking/cleaning/tightening the terminals annually? I don’t think I have had an automotive lead-acid battery make it through a four-year warranty in about twenty years. I had one die this summer that was less than two years old, which had never been run down except in its death throes.

Temperature exposure (mostly heat, but also cold starting), rigidity of mounting interface, starter quality, size of battery vs size of engine/starting load, quality of purchased battery, and general condition/design of a vehicle’s electronics system will all affect battery lifespan.

Edit: and faulty alternators or voltage regulators will damage batteries.

That’s 1 on the list.

Number 2 is knowing how to read the manufacturing date stamped on the battery and never buy a battery that’s been sitting on the shelf for a year. I never settle for one that’s more than 2 months old.

If you don’t inspect and buy your own batteries (e.g. just take it to a service center), you’re gonna get their older stock.

and checking/cleaning/tightening the terminals annually?

Yes, but not just the terminals: I clean the entire top of the battery.

Plus checking the voltage once in a while and topping it off with a battery charger if necessary.

I don’t think I have had an automotive lead-acid battery make it through a four-year warranty in about twenty years. I had one die this summer that was less than two years old, which had never been run down except in its death throes.


Is my experience really the exception?

And we get oven summers and polar winters here. The worst of both worlds.

Back to the bulge: Often a physical failure* within a cell causes an internal short-circuit, the energy released causes heat, the heat softens the case a little, the gas pressure bulges the case, and internal ‘stuff’ shifts around and maintains the bulge. Not all of these every time, but usually.

The battery has failed. Definitely do not use it. Store it as a hazardous material until it can be recycled.

*Others have enumerated possible causes; vibration is most common.

Not for me. I routinely see well over 5 years on a battery, often more. Then again, I buy top-quality batteries. There is absolutely a difference, and you pay for it.

Indeed, I have one SLA battery that I bought used in 1995 that was taken from telecom service that powered my garden tractor starter until just this year. I did take exceptional care of this battery, and it did lose significant capacity over the years, but not enough to affect its usefulness. That’s well over 25 years.

A student said that the battery that bulged was accidentally plugged in to another battery on the cart rather than the trickle-charger. These all had Anderson connectors.
So, I am guessing the fully-charged battery must have delivered too quick of a charge to the partly-depleted battery. The gasses generated too quickly for the vents to relieve and the side walls took the expansion by deforming.
All-in-all everything “worked” very well, but I was very nervous handling the bulging battery until it could be properly contained and removed.
I will use this as an important lesson in safety to double-check, personally, the battery cart.
What do you think? Have you heard of anything like this?
Thank you.

Another +1. A properly functioning modern charger will NEVER overcharge the battery.

Outgassing is caused by overcharging.

Conclusion: A properly functioning modern charger will NEVER cause outgassing.

“can”! Is that a .0001% chance?

I have charged an ES17-12 battery at 40 amps between 25% and 75% full and then allowed the automatic staging to finish the job. This battery worked fine afterwards. (Yes, I hear you thinking, there may be an ever so slight reduction in lifetime. More if you do it more often. And, yes, it did get warm.)
NOTE: This is not permitted for batteries used in FRC robots. R41 permits 6 AMPs. I am not using this battery for FRC robots.

IIRC 6a can be applied to these batteries almost indefinitely without issue. 6a is the safe charge limit for this capacity of lead acid batteries.

Agree on everything, though I’d suggest the lifespan is dependent on a few things:

  • Matches. Simbotics played 66 official matches when they won Championship in 2008. 3940 played 56 last season during a banner-free year that never left the state of Indiana.
  • Wheel choice. Bigger wheels, generally, means more torque–and higher current draw if you don’t plan accordingly. Grippier wheels (especially pneumatic ones) mean more friction and higher current draw. Put the two together, and you have a lot of dead robots deep in the 2016 season. I was working at the AndyMark booth and had teams asking us about this a fair bit. First question: “How old are your batteries?” That’s why you’ve seen those blue stickers in the box with batteries from them with a blank to write down in-service date–helping people track it is step one.
  • Storage and handling. If you leave them discharged all summer, yeah it’s gonna sting. If you do stupid things like dropping them or carrying by the wires (which you should never ever ever do), you’re only shortening the lifespan.

For most teams these days, I think two seasons is a good run and anything extra you get out of it is gravy. My team plays a much lighter schedule so we can usually get longer out of it, but we’ve started logging Rint readings from a Battery Beak (in Sharpie on one side of the battery) so we can track internal resistance and degradation over time. Once it gets up to about 50-75% higher than new (and measured with the same battery cable the whole time), it’ll be time to demote it to pit/practice/inverter duty.

Also, we got one of these really big bags of baking soda. We didn’t feel confident that a regular grocery store box would handle the job in a significant spill, and at six bucks it’s cheap insurance. It lives in a five-gallon bucket in our shop, and if we need to use it the battery goes back in that bucket.