The OE low voltage battery is covered by the new vehicle 4 year / 50k mile warranty; Tesla will replace at no cost if the low voltage battery fails within the warranty period. If your Tesla Model Y has the older 12V lead-acid battery then you can change it yourself (or have Tesla Mobile Service install the replacement). The price (may be out of date) was $85 (battery only), $135 (with Tesla Mobile Service installation). If your Tesla Model Y has the newer 15.5V low voltage lithium battery module instead of the 12V lead-acid battery then Tesla Service or Tesla Mobile Service would replace.