Rechargeable Battery Types in Home Appliances and Gadgets
Type of rechargeable battery, its size, voltage and capacity, determine how long will device operate on a single battery charge.
Features and Specifications
Home appliances and gadgets range from small cellphones and other handheld gadgets to small electric toy-cars and carts. Battery types play significant role in performances of such electric and electronic devices. Type of the battery determines:
- power to weight ratio – it is usually given in W/g or kW/kg. It shows maximum power that battery can reliably provide, without adverse effects on the battery itself.
- discharging current – maximum current that battery can provide for certain period of time. Maximum discharge current is often given in the ‘capacities’ of the battery, for example, 10 Ah battery with maximum current of 30C, can safely provide 300 Amps. Maximum current of car batteries is often given as maximum current that a new, fully charged, 12V battery can deliver for 30 seconds, with the battery voltage not falling below 7.2V. This value is measured at different temperatures and hence have different name: Cranking Amps (CA) when test is done at 32°F (0°C), Cold Cranking Amps (CCA) when test is done at 0°F (-18°C) and Hot Cranking Amps (HCA) when test is done at 80°F (27°C).
- capacity to weight ratio – relative capacity of the battery given in the Ah/kg or more often in Wh/kg.
- energy to weight ratio – relative amount of energy stored in the battery and is given as VAh/kg (Volt Ampere Hours per kg), or as J/kg (Joules per kg).
- operating time of the unit/gadget on the single battery charge. It can be given in seconds, minutes, hours, days etc. depending on the device. Power tools, cordless vacuums and similar electric devices can operate for tens of minutes continuously on the single charge, while smartphones and similar devices can operate for days on the single battery charge.
- weight of battery pack for required performances – for example, if the battery pack must supply 100 W for 20 minutes (cordless vacuum, for example), this is the minimum weight of the battery pack and is given in grams, ounces, pounds or even kilograms.
- recharging time – time required for the battery to be fully charged after being discharged to safe level. For example, deep cycle lead acid batteries should not be discharged below 20-25%, while starting lead acid batteries should not be discharged below 40-50%, on the regular basis. On the other hand, when being monitored by protective circuitry, lithium batteries can be almost fully discharged, without the danger of cell reversal or any other adverse effect on the battery. However, fully discharging lithium battery without protective circuitry can easily damage such battery.
Modern home appliances and gadgets mostly use these battery types:
Lead Acid Batteries
Lead acid batteries are one of the oldest types of rechargeable batteries. They have low capacity to weight ratio and they are used in applications where weight of battery pack is not critical, like car starting batteries, UPS batteries, cart batteries and similar. One of the great things about lead acid batteries is that they are easily connected in parallel to achieve higher capacity and in series to achieve higher voltage.
While flooded or wet lead acid batteries are still commonly used in the cars, home appliances use Sealed Lead Acid (SLA) batteries like gel-cell or Absorbed Glass Mat (AGM) batteries. They can operate in any position, without the danger of spilling the acid around.
Capacity to weight ratio of these batteries is rarely above 35-40 Wh/kg, when being discharged for 20h with constant current. Their capacity is decreased significantly when they are discharged with high currents.
Lead acid batteries are not ecological friendly, but they are almost 100% recycled.
NiCd or Nickel Cadmium
NiCd batteries are not found very often in modern devices, but they provide very high power for relatively short period of time. They can be recharged relatively quickly, but that significantly shorten their possible number of recharges. They are prone to memory effect and have other disadvantages that make them less favorable choice when compared with newer battery technologies.
Capacity to weight ratio is rarely above 40-45 Wh/kg; significantly less when high discharge currents are used.
Due to cadmium, NiCd batteries are far from being ecologically friendly.
NiMh, Nickel Metal Hydride
NiMh don't use cadmium or lead at all, they store more energy per weight of the battery, they can be recharged rather quickly (depending on the type of NiMh battery), don't have memory effect, at least not as NiCd batteries and can withstand much more charge/recharge cycles than NiCd batteries. They don't like to be drained with high currents, but newer NiMh batteries are comparable to NiCd batteries even in segment of discharging currents.
Self-discharge rate of NiMH batteries has decreased over the years and newer batteries can lay around for months without significantly losing the charge.
Capacity to weight ratio is rarely above 120 Wh/kg; high discharge current batteries have capacity up to 80 Wh/kg, rarely above that.
Lithium-ion and lithium ion polymer batteries have the best capacity vs. mass ratio, they have no memory effect, can be discharged with relatively high currents and if proper chargers/dischargers are used, they last long. One the other hand, they are one of the most expensive types of batteries used in cordless devices.
Capacity to weight ratio goes even above 175 Wh/kg, but what you get is what you pay for (not always other way around), especially for batteries used in remote controlled models of electric airplanes and electric helicopters – these batteries cost much more than NiMH batteries.
Lithium batteries come as custom battery packs with cordless devices or as battery packs made from standard size batteries like 18650/19670 lithium 3.7V battery.
There are also other types of rechargeable batteries found at home, but their use is rare.
Nowadays, NiMh batteries are used most often, although, lithium batteries are more and more present in today's cordless devices.
Note: never, but really never short-circuit a battery (of any kind), never throw them in fire or charge them with wrong charger. And when the batteries are dead, recycle them properly.