I was in to multi-engine models with K&B 61's about 15 to 20 years ago until I switched to gas powered 50cc engines. The most engines I had packed on to a model was three and I was trying to design a four engine plane until I realized that the size was too big. The one thing I always adhered to is if one engine quit, I idled back the other one ASAP because, unlike full size aircraft where you immediately know which engine is still running, you can't tell with models. The big problem is that you can't turn in to the bad engine because in you shall go. If you are going to use one ignition battery for both engines this may help save an airplane when it fails. But with like all batteries, the regular monitoring of a battery's capacity and it's voltage would normally prevent this. In any case, don't think a battery as an open circuit. They all have a resistance associated with them. This means that you are actually connecting the ignitions modules together and that may be your biggest problem. Get in touch with an electrical engineer at your field who is familar with these high voltages generated by the modules and ask him what he thinks before you do it. Please post some images of your project. Since the small displacement gas engines have come out my interest has been renewed. Here's an image of me taken about 20 years ago with one of my planes. Dan.