Cordless Drill Batteries are rated not only by voltage but also by amp-hours, which greatly affect how long you can use the Cordless Drill before recharging it. Lower amp-hours make the Cordless Drill lighter and more compact as well as less expensive, but lessen the runtime. The type of battery affects runtime and price.
NiCad batteries cost the least but are the least environmentally friendly and that is because their manufacture releases cadmium. NiCad batteries require careful recycling to prevent contamination of soil and groundwater. They lose their charge in storage, and it can be tricky to maintain them properly through a lot of recharging cycles. The one advantage of the NiCad battery is that they work well in very cold weather.
NiMH batteries have a longer runtime between charges and are considered more environmentally friendly. To work at full power in very cold weather they need a few minutes of recharging to heat them up.
Lithium-ion batteries are smaller and lighter, so you get more power with less weight. A twenty eight volt lithium-ion cordless drill may weigh as little as an eighteen volt NiCad drill. Lithium-ion batteries have a long runtime, keep their charge for a very long time between uses and have a longer lifetime without any memory effect. They are also designed to keep the cordless drill running at full power up to the very last second of battery charge, and work well in cold weather.