I would think you would shoot for at least 700 cca. If you have a demmanding audio system, I would opt for an Optima gel cell. I've had a few yellow tops, and they have served me well. When it comes time to replace mine, I'll buy another. The e36's cargo bay should be accomocating enough for one no problem. The beauty of these are that they have plenty of juice (850cca) and have seperate side mounted terminals for Amp leads.