Warning: Long Post
Hi John,
Sorry that you have had this happen to you, it is unusual and like others I wonder what the cause was.
I have the same battery (2 in fact) Halfords HLB 681 115amp flooded wet cell - rebranded YUASA's.
There could have been a manufacturing defect but I think it less than likely in this case, Yuasa have a good reputation and I have confidence in this battery and would recommend it for various reasons.
You mentioned the Halfords stickers covering the electrolyte inspection ports, the first of my batteries had the same fault, the second did not, I am guessing in the rebranding that Halfords made a not inconsequential error. Only my curiosity led me to peeling back the sticker to reveal the inspection caps.
I do wonder why the battery did not vent off excess gases, there is one open vent port at the top of the positive terminal end side, what appears to be a vent port on the negative terminal end side of the battery is blanked off, I keep meaning to ask Halfords why this is?
Was the vent port obstructed on your battery?
Given that you (and I assume others) were not in the process of charging the battery or using it to top up another battery using jump leads or similar and that there were no tools present to effect a short across the battery terminals then some causes can be ruled out with regard to an ignition source.
A sudden and catastrophic failure could have occurred owing to the internal plates flexing and contacting with an ensuing internal short, from what I understand this is unlikely as that situation arises mostly "
during the extreme current drain initiated whenever you crank the starter motor" for example.
Another possibility is incorrect charging, I am assuming two things here, one that the caravan was not on EHU and two, the solar panel(s) were connected to provide charge to the battery.
Extracts from other sources:
A battery charger itself can be the source of the ignition or the pressure build up of the hydrogen gas that can cause a battery case to rupture.
During charging, car batteries generate a highly explosive mixture of hydrogen and oxygen.
In such cases the battery life is affected and the active material from the plates start shedding creating an internal short. The internal short causes heat and explosion. In this case the internal short is not because of a manufacturing defect but due to incorrect charger selection.
I have looked at the pictures and there may be some indicators therein, I am not about to make any criticisms, everything I note is typically and widely found in most battery compartments.
The battery terminal posts are for the most part 'clean', reducing the likelihood of electrical arcing.
The quick connect type battery connectors I regard as suspect ( I had them in the past and I was not at all impressed with them). The cable connectors could be tidier, i.e. stray frayed and exposed strands (I know I am being picky-just looking for possible sources of ignition).
There is also the possibility of static electricity being the source of ignition. I guess we will never know on that one.
If I were to hazard a guess I would suspect the solar panel charge controller and the quick connect battery connectors and associated cabling.
If I remember correctly you have a PWM controller, I have one also and use it for specific purposes, PWM's are typically of cheap construction (not all are I acknowledge), I use my very cheap PWM in relatively controlled circumstances, I would not rely on it to be permanently connected and left unattended such as in a caravan in storage.
Further, many PWM's have settings for different battery types, typically few people are aware of this and few people make the appropriate settings adjustments, another scenario that sometimes occurs is when a PWM has been set to the parameter for a specific battery type and is not reconfigured when a new battery of a different type is installed.
A possible cause in your unfortunate circumstance is that your PWM controller failed causing excess charge to be delivered to the battery, causing swelling and sudden rupture of the battery casing resulting in explosive gases to be released, the sudden rupture of the battery may have caused sufficient movement at the battery connectors resulting in an arc that was the source of ignition.
I changed my quick connect terminals for an improved design, there are several very good options available for less than £12.00.
I use a good quality MPPT controller in my caravan, I fitted an isolator switch and when solar charging of the battery is not absolutely necessary I turn it off.
One could also fit a battery overcharge safety device as an extra precaution for unattended batteries.
I also note the broken antenna connector, could this have been the source of ignition?
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