Lithium Ion batteries last much longer than lead acid batteries. Typically a lead acid battery needs to be replaced after 200-300 charges, whilst a Lithium Ion battery is likely to last between 500-2000 charges, depending on battery quality, and that's only set to increase with new batteries claiming a service life of up to 12 years. Charging is also a lot more efficient, with a fast charger able to fill up an e-bike battery in just a few hours. The only major downside to Lithium Ion batteries is that the charging process needs to be more carefully regulated to avoid damaging the cells, and that adds a little bit to the overall cost. Normally the electronics needed to control the charge are added into the the battery unit.