Well, it's been talked about, questions have been asked, the why's and why not's etc... So, I have my test battery in hand, I have been experimenting with it. Lithium Iron Phosphate. It should be a direct plug and play drop in battery by the time I'm done. I will update here with the details. My next step is installing it in the car and seeing what happens. My only concern, is how the MS charges the Aux battery. Only when it gets to a certain voltage? Or just tops it off regularly. Because, Lithium keeps it's voltage up until it's just about had it, my only concern is that by the time the car senses that the battery is low, it's already too low for the car to start the charge, and will require external charging. The battery I am testing is 28 Amp Hours. I'm told the Lead Acid Aux battery is 30 amp hours. That will not make a difference as the Lithium is more Efficent to begin with. This battery actually had enough cranking amps to start my work truck, and thats the best it has ever cranked in it's life, and I am also looking into using them for the Scooters I sell. The Lead Acid Batteries in the MS are about 28-32 Lbs in weight, my lithium replacement is about 3-4 lbs. I get my MS60 back from Villa Park service center Wednesday, will need to give back the MS P85 But am installing it and starting testing in real world once I get my MS60 back. I will update, and will offer for purchase if/when my testing is complete and if successful!