An 18" battery (if that's actual length of the ???H8 battery they brought out)...would fit. BTW, which H8 battery did they pull? The Duralast H8 Gold (which is a lead-acid battery), or the Duralast H8 Platinum (which is an AGM battery)? Or did they pull Duralast 95R or H9 battery? Those tend to be the longest.
The
49/H8 &
95/H9 batteries are what I normally recommend because of not only their height & length, but their other specs are usually the same or better than the original battery:
- RC - reserve capacity (usually 100 min +)
- CA - cranking amps (usually 850+)
- CCA - cold cranking ams (usually 850+)
- Ah - amp hour (usually 80, 90, or 100 Ah)
If the aforementioned battery sizes aren't available for some reason, you could also look for a
47/48/H6 or
93/94/H7 class size battery. Their specs my be slightly lower than the 49/H8/95/H9 and may only have 70 or 80 amp hours.
You really don't require more info or a "specific" battery because ALL 49/H8 or 95/H9 batteries will fit. Its an industry standard...these are the size batteries that will fit in your battery compartment. The compartment has multiple hold down points to accommodate various length batteries.
If you look to the right of the long bolt that secures the hold down clamp, you'll see approx 2 or 3 additional threaded holes on the bottom of the compartment:
As far as venting...not sure why no one at a battery store knew this infomation. Batteries either vent from the side or the top center. If the design of the battery vents from the top center, then you'll need the vent kit to extend over to the side of the battery. If the battery vents from the side, then just use the little elbow that came originally with your BMW.
Since not all cars require battery venting...the side vented batteries are usually sealed over with a thin piece of plastic, and you just pierce thru it when you hook up the little elbow. You can see the little round hole on the side of this EvertStart Maxx battery below (Walmart):
If the battery vents from the top...it will be designed like in the illustration below and the pic of the Interstate MTP-93 battery...and the vent hole is just above the word PROPOSITION on the Duralast 49 DL: