I spent some time doing R&D on a Model S, this R&D was specifically on the 12V AGM battery, we tracked the voltage of that battery for one continuous week and the results were surprising: Maximum Voltage was 15.93V, Minimum Voltage was 12.23V and average was about 13.43V... Now the most interesting thing I noticed is that the battery is cycled, several times a day, it is allowed to drop down to ~12.4V and then recharged to ~14.8V, every time it does this it is effectively adding 1 cycle to the battery and reducing its life by 1 cycle... I think we have found the reason for the 12V accessory batteries failing at a higher than expected rate! Obviously I didn't just do this testing so I can talk about it but not do anything about it though! I have been working for months on a solution and we are getting very close to having this solution available to everyone (including Tesla if they would like to team up on this!)... The solution is a Lithium battery pack to replace the AGM, Lithium is better suited to cycling and will last significantly longer under these usage patterns! The major drawback for most vehicles is the cost, however with the Tesla batteries being as challenging as they are to access the cost of replacing a battery (time/money) off-sets a lot of the initial investment... If anyone is interested in this solution please contact me, I don't have pricing pegged down yet because packaging is still a question mark but I'm estimating it'll be around $400 for a 30Ah Lithium battery pack comprised of very high quality LG battery cells! (incidentally the battery will only weigh about 5lbs, we are thinking of packaging in carbon fiber) I am not just posting to advertise, I'm posting for feedback and ideas, I've presented what data I have but I'd love to see what data everyone else out there has? (on voltages, amperages, etc) Does this seem like a good viable solution to you? Does the anyone know what the stock 12V AGM battery weighs? (I'm estimating about 25lbs) Does anyone know what Tesla warranties their 12V battery for? Cost for a 12V battery swap? Thank you all for your help and discussion!