When you’re looking at wiring batteries in parallel, you can hook up a deep cycle battery to a starting battery of the same chemistry. That means if you have a lead-acid deep cycle battery, you want to make sure your starting battery is also a lead-acid battery. Different battery types have different charging requirements, so hooking two different types up in parallel or in a series will not allow you to effectively charge them up at the same rate or capacity. You’ll end up with a damaged battery or one battery that’s full and another that’s not.