After thinking about doing this for a long time I finally put a system together. Its extremely simple, actually overly simple. There are still a ton of things to work out but. . . it works. The basic set up is this, 3 x 48V DC power supplies plus 2 x 12V battery float chargers hooked up in series to get about 168V. There is a diode to prevent current from flowing out of the car battery too and that drops it to about 167V. Is this safe? Well, I took several readings of the battery charge and saw it up to 170V( and as low as 145V.) If it normall goes to 170 then 167 should be safe (I think.) The MAJOR problem is that I'm bypassing the battery control module and it doesn't know that the battery is being charged. After starting the car and driving a few minutes the battery control module realizes that the battery is full and resets the state of charge (SOC) to full. To take advantage of the charge I have been driving in higher gear, lower RPMs more battery assist and coasting in neutral the last few miles before home instead of allowing parasitic hidden charging/ normal cruising charging. The power supplies are only 0.3 amps so I'm charging the battery very slowly (hopefully safer.) Also, you can't just hook the positive connection to the top of the battery pack unless you always leave the car on. I have it hooked up to some resistor thing down below (I have no idea what it is but it reads 160ish V when the car is off.) I'm sure I'm going to get a ton of comments about this especially admonishing my bypassing the BCM. The BCM and SOC are not so good in the first place. I always got low voltage SOC resets in the past so I wouldn't be surprised if the SOC is more accurate after a little plug in charging. I will add more info later, just excited about this and wanted to post. I have had it on for only 2 days and driven about 200 miles. The mpg increase is slight so far.