In performance and real life usability for lead acids that are vehicle starter batteries, they only use 30% of the stated amp hours or stated as “30% depth of discharge” before the voltage drops so low you can not start your vehicle. So only 30% of its amp hours are usable, whereas lithium batteries have a 98% depth of discharge. For example, our ETX36 is a replacement for an YTX20 Yuasa series, which has 18ah rating of capacity. The amount of actual useable amp hour is (18ah x .3 = 5.4ah). We use a 12.4ah cell in our ETX36 which is actually 7 amp hours MORE than the lead acid battery we are replacing.