You might want to keep that battery as a story piece in your garage to remind yourself how ***** can happen.

lol!

Optima. wants a special type of "Battery Tender" (float charger) - old thread on that, IIRC posts are by Optima Jim

you will need to very carefully clean out & flush out every tiny nook & cranny - & be SURE it did not get inside the unit body - if it did, you will likely need to drill some holes to get at it

every 1/2 year for the next few years you will want to check and be sure that the acid did not get in and weaken the front suspension -- you know, the stuff that holds the car up and the wheels on...

I see a repaint of that corner in your future.

at least it cannot reproduce and multiply like Ebola virus...

Wow! That really went up. Low electrolyte level from lengthy charging and an internal plate failing could cause a short when big current was drawn to run the starter motor. Having the charger on and connected may have added even more juice. If you weren't fiddling with the charger cables and the trunk was open then the fire probably started inside of the battery. I'm glad it didn't go up in your face. Hmm, a loose ground connector also could have sparked on startup.

Neutralize, rinse, repeat, repeat...........................

My 88 Carrera has very little current draw when parked. Just the clock is running. It can sit 4-8 weeks or more with no apparent loss of battery charge and the battery is at least 7 years old. I don't feel that I need a battery tender. You could also disconnect the ground cable or install a cutoff switch when storing.

Never have had a charger on mine. Park it from Nov. to March. Leave it hooked up too.
I start it once in a while to move it around to work on it but that's it.

1988 911 battery exploded
 

So I was driving my 911 down the highway after jump starting it from a drained battery. About a half hour into the drive a big BANG and spark seen in speedometer and tech clouds up. Pull over and realize battery completely exploded.

So replaced battery, car cranks but will not start. Anyone care to jump in here and let me know what could be the problem? Shop has had it for two days and claim they can not find why it will not start.

Fuses and relays all removed cleaned and tightened? Grounds too?
Massive spike in voltage to the CDI has fried it?

See if you have power to the fuel pump, if not maybe the DME relay under the drivers seat is bad. The ECU under the drivers seat provides the signal to the coil. If you saw sparks in the speedometer, better check EVERYTHING.
Good luck. What is your location?

Mike

Ya, Pete, but your garage is so big that it gets fully warmed up just driving from one corner to the other in there.

I don't leave mine over night without a tender on it - got to keep the clock accurate, you know.

Bla Bla Bla

You really have a way with words!

Is this true? I've started mine a few times with the charger still attached and no problems...

The issue with leaving the charger attached is likely due to battery outgassing in tight confines with little ventilation like when the hood remains shut etc. The sudden load on a not-so-good connection at charger leads could result in spark. Basically the charger makers are covering their behinds here. Use common sense and you'll be fine.

Also, the battery hold down importance shouldn't be underestimated. If battery is allowed to flop around the vibration could cause plates to loosen and internal shorting will result.

My '03 540 uses battery with a vent tube to help reduce gas build up. Not sure if can/should be adapted to the 911. $13 on the bay.

Battery Relief Breather Vent Tube Line Kit Set New for 82 10 BMW Models | eBay