Car batteries will produce explosive ( and corrosive and unpleasant smelling) gas. Even maintenance free batteries DO vent HYDROGEN GAS. You need a Gel tyle battery or a battery specifically designed to allow for a vent tube to the outside of the car! I'd exchange it - they should let you do so if you approach the problem from a SAFETY standpoint. They should know better that to sell a regular battery for a car with an internal battery!

This optima post is helpful.
-Tom

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RIP "Betsy" (Oo=*=oO)
'96 E 3 2 0 (W 2 1 0) M 1 0 4 (Totalled)
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2004 Audi A8L
'98 VW Passat 1.8T 5M
'87 Alfa Romeo Milano 2.5L 5M
'67 Impala convertible, 327cid