If you put several batteries in a circuit, they add up their voltages. And empty batteries should be disposed of properly. However, over time, this excess fluid is used up as fluid slowly off-gases hydrogen and oxygen molecules through the vents. Another type of maintenance-free battery is the gel-type battery While these batteries cannot leak or spill fluid and can be installed at odd angles, they do have a weakness. Also, these batteries have a smaller life and are not high powered. Alternatively, lithium ion batteries are lightweight, high powered and do not need to discharge completely before being recharged. With the battery recalls that have recently occurred with both Dell and Apple many people have been writing about battery safety issues. • Batteries can be manufactured under uncontrolled processes.