Get some bicarb and clean it up ASAP. Then pull it apart and find out what the damage is.
When I was an apprentice we had a few Benz batteries go in the same manner, one while a tech had his head under the bonnet. Scary stuff, the plastic went everywhere as did the acid. Luckily we were a mandatory safety glasses shop or it could have been much worse.
2012 Volvo XC60 T6
2008 Child- Female
2002 Ducati 998
1999 RSV Mille
1985 Suzuki RG250
1983 Suzuki RG250 (racebike)
1974 Vespa 150 Super
2x 2004 Cats of mixed breeding
1978 Girlfriend, Polish heritage
No liquid anywhere.. it was a sealed battery.. New one in today and she fired right up!! Cheapo battery's only last so long.. However it lasted a LOT longer then the spendy one I had last time..