The AAA NiMH battery is an alternative to the older nickel-cadmium (NiCd / NiCad) AAA batteries. It is desirable to reduce the use of NiCd / NiCad batteries, since cadmium is a highly toxic substance that is dangerous for humans as well as for other organisms. Today, most areas have rules and regulations regarding the safe disposal of used NiCd / NiCad batteries, but many NiCd / NiCad batteries still slips through the net and end up in landfills and similar places from where cadmium is slowly released into the ecosystem.

The metal in an AAA NiMH battery is in the form of an intermetallic compound. When you charge an AAA NiMH battery, the voltage will force hydrogen ions out of the potassium hydroxide electrolyte solution. When you place your AAA NiMH batteries in an electrical device they provide power to the device and as the AAA NiMH battery slowly discharge the same hydrogen ions will be released again and participate in the reverse action. The intermetallic compound found in an AAA NiMH battery can be of several types. The most popular compound is called AB 5 and is a mixture between nickel, manganese, cobalt and/or aluminium and titanium. AB 5 also always include so called “rare earth compounds”. One other frequently used compound in AAA NiMH batteries is AB 2. This compound creates an AAA NiMH battery with a higher capacity than the AB 5 compound. AB 2 is based on titanium and/or vanadium with the addition of zirconium or nickel, modified with iron, chromium, cobalt, and/or manganese.

AAA NiMH batterycanbecome overcharged and it is therefore a good idea to use a battery charger that is microprocessor controlled if you are fast charging your AAA NiMH batteries. These battery chargers are often referred to as “intelligent battery chargers”. Modern AAA NiMH batteries are much safer than the first NiMH batteries when it comes to overcharging, since the modern AAA NiMH battery always contains a catalyst. This catalyst defuses any harmful gases that can develop as a result of overcharging. Hydrogen and oxygen gas will with the aid of this catalyst quickly form harmless water molecules. The reaction will however release energy and the AAA NiMH batteries can become quite warm during the end of the charging process. Some very quick chargers are therefore equipped with fans that make sure that the AAA NiMH batteries never turn to hot.

AAA NiMH batteries have a self discharge rate that is a higher than that of the NiCd / NiCad AAA batteries, 30% per month compared to 20% per month. You can however reduce the discharge rate significantly by not storing your AAA NiMH batteries at extreme temperatures. If you want to store your AAA NiMH batteries for a long time, it is advisable to give them a charge around 40%. One other disadvantage compared to the NiCd / NiCad AAA batteries is that the AAA NiMH batteries are more high-priced than the NiCd / NiCad batteries. On the other hand, AAA NiMH batteries are capable of providing high rates of discharge for a few seconds at a time throughout their whole discharge cycle. A NiCd / NiCad AAA battery is more unstable and will begin with a very strong battery strength that then gradually decreases when the battery is used in an electrical device. AAA NiMH batteries will stay strong until they are on the brink of being completely empty and then quickly drop.