Battery go BOOM!
 

Latest issue: Recent replacement of dist cap, rotor, ICU (ICU seemed to fix non-start issue, but engine now smoking - see other post).

Battery been on charger. Went to crank & soon as I turned key, BOOM!
Blew couple holes in plastic top of battery, sides cracked etc.
Tried to clean up w baking soda / water.

WTF?

Ragtopper
1982 380SL

Batteries emit hydrogen gas when charging. Hydrogen has a very wide range of air to gas ratio at which it will explode. There was likely a tiny arc at the connection and it exploded. This is one of the reasons to wear eye protection around batteries. Heard one explode decades ago inside the shop while charging, still remember it well.

Over the years I've had a couple of batteries explode when put under a load. These were not recently charged so hydrogen escaping the battery wasn't an issue. Internal connections can fail , arc and light off hydrogen was was internal to the battery.

How long was the battery charging? I'm wondering if the battery was failing and was ovecharged.

97 - yes. I keep charger on it as it has parasitic drain. Perhaps an overcharged low battery.
Anyone suspect collateral damage?

Ragtopper
1982 380SL

How big of a charger ( Amp rating ) ?

What actually matters is charging voltage when connected to a fully charged battery, but amp rating is an easy way to quantify. Measuring charger voltage without it being attached to a battery won't tell you much.

You don't want to have a battery charging over 14.6 or so V , anything approaching 15 it too high and will boil a battery. Note, charging voltage will be higher than battery open circuit voltage, this is normal.

A trickle charger at sub 1 amp does not put out enough power to cause a problem, a 10 amp non automatic charger can lead to boiling / excessive gassing.

And, for the record you can measure state of charge ( how full the gas tank is ) on a lead acid battery that has not been charged / discharged in the past 8 hr or so. Voltages will vary a bit so use it as a general guide. To measure battery capacity ( how large the gas tank is ) you must do a load test.

12.66 V 100 % Voltage much higher than this indicates an overcharge condition.
12.42 V 75 %
12.18 V 50 %
11.94 V 25 % Going lower than this frequently will damage a battery designed for starting
11.70 V 0 % Full discharge , going lower will damage the battery