There's no point in comparing batteries unless you understand how much energy they can hold, and how much you need.

Battery capacity is usually expressed in kilowatt-hours. For each mile you move the car, you need roughly on third of a kilowatt-hour (0.33 kW∙h)... so for 50 miles, you need at least 16 kW∙h. To calculate the approximate energy capacity of a battery if it is not provided, you can multiply the battery voltage by the capacity in amp-hours... if the amp-hour capacity is known.

For instance, eight lead-acid batteries at 12 volts and 100 amp-hours each (a common size) would have a nominal capacity of 10,000 watt-hours, or 10 kW∙h. Unfortunately, that capacity is determined under conditions in which they are discharged slowly; when they are discharged quickly (providing the high power needed by a car), their capacity is greatly reduced, especially in the case of lead-acids.

**Non-plug-in hybrids** only use the battery to store enough energy to move the car for a few seconds - they have a battery which is usually around one kW∙h. They're generally useless in an EV, unless you want to combine a dozen or more of them.

**Plug-in hybrids** typically have 8 to 16 kW∙h of battery. The biggest ones can be just enough to provide somewhat useful range in a typical EV, but since the manufacturers of hybrid vehicles typically can't make them go more than 50 miles on the battery charge, a DIY conversion of the same size of car won't make it that far, either. The Chevrolet Volt battery is a popular example; a Volt has an electric range of 53 miles, with a much more advanced motor and other components than a DC DIY conversion would typically use.

The obvious source of a large enough battery for an EV is salvaging one from another EV (such as the Leaf or Tesla already mentioned). The battery (or battery pack, as it is composed of several modules) is as large as over 100 kW∙h in some EVs, and useful EVs start at about 24 kW∙h for smaller cars with moderate range.