BrockWI wrote:After a while with the new larger battery in there I have noticed some interesting things. When the car is bulk charging the 12v aux battery it sits a the top end voltage a LOT longer.
I noticed the same thing when I replaced the original battery in my 2011 with an Optima AGM deep cycle (Yellow Top) of the original size. That Optima was still performing like new when the car met its demise 13 months after installing it. Unfortunately, the insurance company's storage yard would not let me keep the battery when I went to look at the car and make sure I got everything out of it. The original Nissan flooded cell batteries have relatively high internal resistance when new and get higher as they age. This makes the DC-DC converter drop back to float sooner than it should. The lower internal resistance of the AGM battery allows it to charge to a higher SOC before the DC-DC converter drops back to float. As soon as the Nissan flooded cell battery in the 2015 starts getting weak, I will replace it with an AGM even if it is still under warranty.
As you are seeing, there is no problem with the charging algorithm of the DC-DC converter when it is charging a battery with low internal resistance.