Right first things first the chemistry of the battery is simply what its made of inside. There are several different types of battery but the most common one is lithium-ion which is usually abbreviated to li-ion. If the battery is lithium-ion (li-ion) its the best battery on the market these do not carry any memory effect and will keep the same charge how ever many times you charge it. They also have a slow loss of charge when not in use. Please dont forget that most batteries will not last forever and there will be a decrease in power up time over the usage of the battery. Example; A laptop that is full most of the time will loose roughly 20% of its battery life every year. As for chemistry thats all you really need to worry about as most rechargeable batteries these day are made using li-ion as it carries more advantages over other chemicals.
Next thing Volts is basically the pressure that is needed to keep that item running its pretty much standard for most things and if you choose the right battery model its nothing to worry about.
Now Capacity this is a big thing to look for when choosing a battery, many cameras and camcorder batteries come in different capacities but will fit the same camera or camcorder for instance the SONY DCR-SR57 camcorder can take 3 different batteries NP-FH50, NP-FH70, and NP-FH100. Now these three batteries all carry different capacities also so known as mAh (miliamp hour) Basically the higher the mAh the longer the battery will last, so to speak its the fuel to your camera just like a car its how long it will last. This has to be the biggest thing when it come to choosing a battery. So when choosing think to your self if you want a longer lasting battery. So with the example we have
NP-FH50 (900 mAh)
NP-FH70 (1800 mAh)
NP-FH100 (3980 mAh)
Basically as we move down the list you see that every time the battery mAh doubles more a less, which basically means it will last double the time of the previous battery. So if your currently using the NP-FH50 and bought the NP-FH100 it should last 4 times as long so if the NP-FH50 lasts for 1 hour the NP-FH100 will last for 4 hours.
Right i think thats every thing your going to need when it comes down to choosing the right battery but if you have any questions just give us a shout.
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