Lead for fixed installation was a general rule a few years back but it's not really advantageous anymore. There were several concerns with lithium (especially p

Lead for fixed installation was a general rule a few years back but it's not really advantageous anymore. There were several concerns with lithium (especially price, availability and safety) that are now addressed making it much more interesting. For example a powerwall built with LiFePO4 cells will be good for at least 10000 cycles (+15 years) and afterwards the degradation curve is much nicer than lead-acid so you can easily get 25 years if you can cope with some reduction in capacity. It also has no risk of thermal runoff (so it won't start a fire is a cell has a catastrophic failure) which is much better than traditional cobalt or manganese batteries. You can get grade A cells for about ~400$/kWh today when buying only one and obviously bulk discounts are widely available if you are getting something bigger. It still burns if your house catches fire though so that's still a concern.