FAQs and some Myths about Rechargeable Batteries explained
Can 1.2V NiMH batteries be substituted for 1.5V alkaline batteries ?
Yes, for most high drain electronic applications NiMH batteries are ideal substitutes and you needn't worry about the apparent voltage differences. Even though alkaline batteries are rated at a nominal 1.5 volts, they only deliver 1.5 volts when they are fully charged. As they begin to discharge the voltage of alkaline batteries continuously drops. In fact, over the course of their discharge, alkaline batteries actually average about 1.2 volts. The main difference is that an alkaline battery starts at 1.5 volts and gradually drops to less than 1.0 volts. NiMH batteries stay at about 1.2 volts for most of their discharge cycle.
In some cases this may have a small initial effect. A flashlight will initially be a bit brighter with a 1.5V alkaline battery, but once it gets to 50% capacity, it will deliver 1V and less, when it becomes a lot dimmer than the same light with a constant 1.2V supplied by a NiMH rechargeable. The rechargeable battery light will stay a constant brightness for far longer than the standard battery light.
Do NiMH batteries have memory effect?
Technically, NiMH batteries do not have a "memory effect". In practice they can experience minor voltage “depression”. If you use a device such as a flashlight, radio, or digital camera for only a short time every day and then charge the batteries every night, you will need to let the NiMH batteries run down occasionally, or use the discharge function on the charger, say every couple of months.
How many times can a rechargeable battery be recharged?
Simply put - hundreds of times. The technical answer is quite a bit more complex but basically it is better for a NiMH batteries long term life to only partially discharge , then recharge. In practice this may not really worry you, as the batteries life may be increased from 300 recharges to 600 recharges using best practice – it is still very efficient!
Does rapid charging reduce the life of batteries?
No. So long as it is done using a properly designed, smart charger, most NiMH batteries can be recharged in about an hour without any damage or reduction in their life. However, NiMH batteries must be rapid charged with a charger specifically designed for charging NiMH batteries. Chargers designed to charge NiCd batteries can overcharge NiMH batteries. Even a standard or slow NiCd charger can damage NiMH batteries.
Do NiMH rechargeable go flat quickly when not in use – ie do they self discharge?
Years ago this used to be an issue with NiMH rechargeables, however modern rechargeables are mainly produced as “ready to use” ,or, ULSD (Ultra Low Self Discharge). This mean that NiMH batteries are now ready to use straight from the packet and will have months of life in them if sitting idle. All the convenience of a standard battery with the benefits of a rechargeable!
Are standard alkaline batteries “stronger” than rechargeable batteries?
This is a myth supported by disposable battery manufacturers advertising their rated capacity as superior, rather than analyzing the more practical ,but complex to evaluate, actual capacity. AA alkaline batteries have a rated capacity of over 2500mAH and NiMH rechargeables have rated capacities of 1500-2100 mAH, however when it comes down to actual capacity – a rechargeable may run a device far longer than a disposable. The higher the power drain , the better the NiMH battery performs compared to a disposable.
In plain English: In high drain items like digital cameras, high power torches or bike lights in constant mode, a NiMh rechargeable will run on a single charge for 3-4 times as long as a disposable battery!
