Lead acid sucks as a storage battery, but it's hard to beat the safe, reliable, low maintenance, and dependable nature of a lead acid starter battery.
Tesla uses a regular lead starter battery just like everyone else.
To save weight and extend range, Boeing tried to use lithium as starter batteries for the APU on the 787 dreamliner. Even with using a complicated 4-level BMS with internal relay cutoff and dedicated external charrger, they had 2 to catch on fire. Now it is even more complicated with a fully-enclosed battery in a titanium housing with vent tubes. Makes you wonder how much of all that original weight savings has evaporated?