Thank you AMDPower for starting this thread. Lots of great info. After reading everything, I ordered the Ryobi 42inch 100Ah zero-turn yesterday. I'm going to be mowing a lot of lawns with it so I needed to know I could replace the batteries and get more run time. Unfortunately I have neither the time or the expertise to build my own battery, but I don't mind paying for a drop-in solution. My question is, if I went with either 4 12v 100Ah in series or the single 48v 100Ah do I need to change the charger, cables, meter and add some kind of cooling or is it a true drop-in like so many of the batteries advertise. I'm a total noobie when it comes to this stuff. I really just need the easiest solution to get more daily run time. I think somebody mentioned that you would have to charge the 4 12v batteries with 4 separate chargers. I'm probably going to replace the batteries right away as I mow grass for a living and I just don't think the stock run time is going to cut it (pun intended). I was looking at the Mean Green mowers which claim a 7+ hour run time but would end up costing me about 13-14k to purchase and get out to Hawaii, so I can easily justify an extra 2-3k on top of the cost of the Ryobi. Any thoughts would be greatly appreciated.