Lead Acid

Overview

Lead acid batteries are the kinds in cars, motorcycles, and boats. They're big and heavy and if you move them around you'll hear a swishing sound from the acid inside (heavy from the lead). 

The voltage is typically 12V, but that's nominal which is ~50% capacity as shown in the table below. While charging it'll be between 13V and 14V DC. The way you measure it is with no load connected, or with the car / motorcycle turned off completely and then measure the voltage across the terminals and compare with the chart below.

Storage

Lead Acid Batteries are best kept at full charge even for long term storage. This is different from what you are probably used to with lithium batteries, the ones in most electronic devices where you should store them at around 50-75%.

Lithium Ion