Charging batteries on shore power

[YANDINA]

No, that kind of explosion is due to hydrogen build up.
I'm lucky to have my sight, let alone life, I had one explode right in front of me that only just missed. Jumped in the shower to get the acid off. Parts of the battery embedded in the ceiling from the force. It was not on charge at the time, just connecting a radio caused a spark to set it off.

[donradcliffe]

Originally Posted by Nyaminyami

0200 hours, moored in the marina - BOOM!
Woken to find my 12v genset battery had exploded - completely blown the top off, spraying battery acid all over the battery compartment under the steps and a fine acidic mist in the galley.(Used a bicarb solution to neutralise)
A couple of days previously I had cursorily checked the battery and the indicator had shown green and it remained permanently connected to its remote (max 3 metres away) charger drawing from 220v shore power.
Examination of the shattered battery revealed buckled plates (presumably from heat) and the (smart) charger output was only 10.9V
I have assumed that the incident was somehow caused by the charger, having become faulty, had lost its ability to measure battery charge levels and had simply continued to pump in 10.9V even though the battery, being previously held at full (float?)charge, might not be able to take any more charge.
Is this a fair assessment or am I missing something? What lessons can be learned? Are there any fail-safe suggestions out there.
Thanks in advance and greetings all, from Barcelona.

First, you have to realize that all battery problems occur between 0200 and 0400--that's normal battery behavior.

What was the amp rating of the smart charger?

How big was the battery?

Without more information, I'm pretty sure that one of the cells in the battery shorted out, and the battery terminal voltage dropped from 13 volts to 11 volts. The smart charger continued to work, but instead of a float current of an amp or two, it was pouring in max power. That power created a lot of heat in the battery, and it also overcharged the remaining cells, creating hydrogen and oxygen gassing. Given time, parts of the battery around the shorted cell got plenty hot and the gases ignited.

Shorts are rare, but they happen. This can also happen away from shore power if the shorted battery is one of a parallel bank, but it is less likely. It is more likely if you are motoring for a long time and you have the alternator as an energy source.

The solution--its a rare occurrence, but a bigger battery or a smaller charging current would prevent the boom.