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Discussion Starter · #1 ·
A friend of mine that knows very little about EV's asked if I could look at his battery pack. He told me it was leaking what looked like water onto his concrete floor and was now bulged. I knew it was SLA and 2 batteries inside so It would be easy to fix...whatever was going on. He claimed it was all working OK just the night before. Maybe he connected a 48v charger instead of the 24v one?

I wish I had taken pictures of the plastic box before opening it. The 2 SLA's tell the tale well enough. Hopefully this brings a few people a good laugh!

There's 2 of these inside the plastic box. They are wet with battery acid.



I've seen bulged SLA's before, but this is a whole 'nother level of bulged! Clearly they got quite hot too.




 

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Continuing use past EOL wear point can cause any lead chemistry to literally explode

usually when charging but not necessarily

even violently causing lots of damage, acid everywhere

sealed just as much if not more so.

Periodic cap testing, proactive replacement before any outward signs of wear are apparent

is how to avoid such surprises
 

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Discussion Starter · #3 ·
Continuing use past EOL wear point can cause any lead chemistry to literally explode

usually when charging but not necessarily

even violently causing lots of damage, acid everywhere

sealed just as much if not more so.

Periodic cap testing, proactive replacement before any outward signs of wear are apparent

is how to avoid such surprises
Yes...sure...for you or me that might be the case, but for a random EV user that has no clue, not likely! In this case, my friend had no idea about what he was doing or what was happening with his batteries.
 

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Just normal overcharging.

Extra energy goes into heat. Heat softens the plastic. Water boils, bursts the cells.

Cylindrical might just be due to unintentional hydroforming, which is going to make anything bulge in a rounded shape.

This can even happen just from chargers without temperature feedback. Max charging voltage drops as temperature goes up, so, a battery is full at a slightly lower voltage, which means the slightly too high voltage now gets dumped as heat, softens plastic, etc.

Seen it on a bunch of them that get pushed to their limits.
 

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If they are sealed, they probably dont vent. Get some plate flake to short a cell and it will get really hot. Just looks like a high rate charge on a going bad thin skinned battery to me. Be happy it wasn't lithium
 

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Those bulges are suspiciously shaped...like there are a half dozen cylindrical Chinesium cells in each brick instead of flat plates.
To me it just looks like the result of the internal dividing walls of the case which separate each battery into six cells. The internal walls are faintly visible in the moulding of the case of the SLA batteries that I have, even in new condition.
 

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This is what happens when you have a truly sealed lead acid (SLA) battery, instead of the preferable valve-regulated lead acid (VRLA) design with a pressure-relief vent. I was surprised to learn that the batteries in our mobility scooter (similar to these) are actually sealed, since the automotive AGM batteries that I previously knew about are valve-regulated.
 

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Discussion Starter · #12 ·
It's hard to tell how many cells are inside. The plastic box they were inside of has ribs to hold the cells and they created bends and markings on the hot plastic. I have a couple more of these batteries and they are 6 cells...like is common to most 12v SLA's. Whether they are a jelly roll or not...that I can't say.

I've never seen an SLA that is commonly used in an EV or a UPS that had vents. I think this is due to the possibility of liquid leaking out of the battery through the vents if it was not vertical. Clearly these ones were not vented. IF they were, I think what was said above about heating would not have cased them to burst like they did.

I can't speak for most people, only for what I can observe. In my opinion (not observation) most people have no clue what they have. They buy a thing (ebike, scooter, etc) and ride it around a little while and think its cool. Then they get bored with it and it sits in the garage or shed for a while. Later the EV comes up in conversation so it gets taken out and charged. By then the batteries are in who knows what state! Since most people are NOT aware of how SLA needs at least a trickle charge to keep alive, those batteries are now probably dead flat. The owner tries to charge them and of course this sort of thing happens from time to time.

I don't know if anyone has looked very closely at electric unicycles or not. I have! I have 2 of them from Gotway and InMotion. I've taken them all apart. Gotway/Sherman are particularly BAD!!! Many lack a proper BMS. They will have over charge protection and balancing, but no way to protect from over loads or low battery or a proper disconnect. As a result, a wheel can sit for long periods of time and slowly discharge its pack down to zero. I think as EUC's age, we will see people doing to them exactly what has happened to so many e-bikes and scooters. They will run down to flat and the owner knowing nothing about what they have will plug it into whatever charger they might have. Some cells will recover and charge and others will simply go thermo nuclear and burst into flames. It's already a random problem that EUC's catch fire while used regularly. I think this is likely to get worse as they age and get neglected.
 

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It's hard to tell how many cells are inside. The plastic box they were inside of has ribs to hold the cells and they created bends and markings on the hot plastic. I have a couple more of these batteries and they are 6 cells...like is common to most 12v SLA's. Whether they are a jelly roll or not...that I can't say.
With a 12 volt nominal voltage, there will be six cells; there must be six in series, and there is not point in parallelled cells. The plates will be flat; the rolled or spiral AGM cells are obvious in the "six-pack" appearance of their case (in 12 V models) - that's the original Optima "Spiralcell" line from half a century ago and still in production (although even Optima is switching to flat in the newest version of their YellowTop dual-purpose line). Exide (under the Orbital and Vortex tradenames) and some Chinese knock-offs ar also spiral-wound, but I think that Optima has always been the only common brand with this construction.

I've never seen an SLA that is commonly used in an EV or a UPS that had vents. I think this is due to the possibility of liquid leaking out of the battery through the vents if it was not vertical. Clearly these ones were not vented.
VRLA batteries can be operated in any orientation, except the one in which the vent faces down; for example, the Trojan Solar AGM line says that the allowed installation orientations are "Horizontal & Vertical". It makes sense to me that in automotive applications where they are mounted in an engine or battery compartment they would be vented, but in applications where they will used in an occupied area without a suitable enclosure they would be sealed.
 
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