I used to run dual batteries in my car as when I got into late rounds seem my battery was always dead. Alt said it was charging...after fighting the issue for many months, finally tested the alt and even though the gauge said it was charging, it actually wasn't, thus the reason the battery would be dead in the late rounds. I have since went back to 1 battery and have been problem free for years. I'm thinking that you may have another issue and by switching to 16 volt may or may not eliminate the issue. How old is the current battery? How about your coil? My dad and sister in law both had coils act up last year. My dad car would start, but was slow to fire. My sister in law coil just took a crap one morning and car wouldn't start. Sometimes its the more simple overlooked things that are the problems.