Today while making a parts run at work I took a short trip down the highway in my 2011 justa. every thing was going great and out of no where POP a large bang from the fire wall followed by a puff of sulfurous smoke from the vents. I rolled off the throttle and looked and found no warning lights. so I worked my way off the highway to a near by parking lot to investigate. Under the hood there was nothing to be seen from underneath I could see liquid dripping down the undercarriage on the passenger side. After a few drops landed on my arm I quickly realized due to the burning that it was acid. So looking in the battery cover I quickly noticed the problem. The battery had exploded. Is this a problem any one else has come across or herd of? in my 15+years of automotive experience I have never seen one blow while on the road. Are there any know problems I should check into such as an overcharging alt or haywire voltage regulator, Or was the battery just low on water and overheated, or does my mini secretly had me and is trying to kill me?

The battery might be the victim, not the villain here if there's something wrong with the charging circuit and it was getting overcharged. Don't just put in a new battery and call it good, have the electrical system checked out.

Also wash down anywhere the battery acid dripped with baking soda and water.

It happens, Google brings up cases and photo's which yours will be added to. Could also be vent tube blockage and pressure built up. Check and see if the car threw out some codes with a OBD reader, maybe voltage related overcharging.

wow, that is quite scary! would like to know how this can happen :O

since the seeing eye popped out it was definitely building up a lot of pressure, could have been way overcharged, vents blocked.

Update: installed new battery today and everything seems fine. I checked the battery with both a old style battery / charging load test and with my scan tool and it is charging At 14.489 volts when running. talked to a few mini techs today and they seem to think the cause was low battery voltage . They ask if it seemed to be starting slow before the battery blew it's lid, which it had. they said that some time if the voltage is low the alt will surge on and off as the alt tries to recharge an already doomed battery. and that they have seen this before once or twice but most only blow the eye out.

Wow, over my lifetime I've owned a lot of different autos. Never seen that happen..

Did you get all that acid washed out of there? Geez, what a mess.

Yeah I sprayed the car down as soon as I got it back to work. then went back out an hour or so later and washed it again with an acid neutralizing spray that we use at work. The good thing is that the battery housing diverts most of the acid away from the engine bay and out the bottom of the car.

One day my alternator stop charging my battery so the battery was running the entire show until it exploded all over my engine bay, I'll never forget it because it was in the middle lane in LA traffic.

14.5 sounds a tad high. You should check it after its been running 10-20 minutes though, it likely does an initial fast charge and then cuts back.

Did you check the breather hose and valve connection on the old battery, that alot of pressure, never seen a BMW / MINI varta battery do that. If the hose was clogged it would have blown off a long time ago.

A 12 volt battery contains 6 2.4 volt cells. That's 14.4 volts. That being said, anything over 14 is high.

Worked at the BMW dealer. Would see this from time to time.
Usually due to small battery containment area, old battery, disconnected vent tube and a loose battery cable.
During a start; a small spark and blammo!!!

A lead acid battery will explode when there is a build up of Hydrogen in the cell chambers and a spark ignites the gas causing the to battery explode. Hydrogen is a chemical by product of the charging process which is the reason of the vent tube. Most people believe that a modern car battery is "maintenance free" but that term should be taken with a "grain of salt". Most batteries will not cause a problem during its lifetime if the car charging system is working ok. But heavy usage and ovecharging a battery will cause the electrolyte to "boil" excessively that can produce low battery levels. The low battery levels is replaced with hydrogen molecules. If there is a sufficient volume of hydrogen in the battery without venting properly it becomes explosive. Remember the "Hindenburg". I regularly check and "top off" my battery cells with distilled water. I would hate to have my battery explode in the MCS since it is mounted inside the the hatch area. And yes this has happened to me when I was younger. I once overcharged my battery with a non-trickle battery charger. I left charging in the car for about 4-6 days, I don't remember how long. But when I tried to start it.... Ka Boommm". What a mess!!