BYI Deep Cycle Lithium Batteries: Made in the USA 52 volt 15 ah and 52 volt 11 ah --- normal lithium batteries (i.e. Lifepo4 etc.) can only use 60--70% of the stored charge (shallow cycle) BYI can use 92--95% of stored charge (DEEP cycle) so you can go much farther on a charge. BYI also charges 50% faster and can be run down all the way every time without damage to battery. All BYI e bike Lithium batteries have a 3 year full warranty and come with high speed smart chargers that auto balance the cells in your battery.