I have a metal detector that takes 2-9 volt batteries to operate,I have a Rayovac Universal Battery Charger that says it’s good for NIMH batteries,I’m looking for a battery that can hold a charge for a long time and be able to be charged in this charger.What are the different kinds of batteries and do they require certain chargers?What battery do you recommended for my application?I’m thinking about getting Rayovac Rechargeable NiMH Battery 175 mah,only because there $ 6 a piece is that a good price,do they last or hold a charge well?How long do regular NIMH batteries last can you store them without using them for a long time and have them remain in good condition?
Thanks Joe and Amy
Best answer about What is the best rechargeable battery for me?
Answer by Joe Lanzendorfer
If it’s an NiMH (nickel-metal-hydride) battery charger, then you should stick with any NiMH rechargable battery. The brand doesn’t really matter, just don’t go some place like radio shack and get ripped off.
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Another word of Rechargeable Battery Charger :typical battery life 9 volt rechargeable metal detector,
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actually there is a difference in batteries. make sure you get NiMH becasue they are made for high drain devices. you would want Nickle Cad for low drain devices. they require different chargers, but you can get a good deal on a charger and batteries at radioshack. plus their associates can answer any other questions you have. also be sure and let the batteries run all the way out before you recharge them, otherwise they wont hold as much of a charge in the future.
Buy rechargeable 9V cells with care. You’re replacing an Alkaline cell with one of these rechargeables, and it’s not a perfect match. Alkaline cells deliver a nominal 1.5V per cell, so a typical 9V snap battery stacks six of these, to deliver a true 9V. NiMh and NiCAD cells are nominally 1.2V, so a 9V cell will stack either six of these, but deliver only 8.4V, or stack seven of these and deliver 9.6V. You should check how tolerant your metal detector is of voltage variations like this, and buy accordingly.
NiMh cells in general do NOT hold a charge for long period of time.. they have a self-discharge issue that means they drop pretty significantly over the course of a week. As long as you can charge your batteries before you go out, you should be fine. NiMh have a higher energy density than NiCAD.. you can actually buy 9V cells at you to 250mAh, though that’s a premium priced cell.
I would tend to avoid NiCAD. A NiCAD cell can probably provide higher peak currents than a NiMh, though modern NiMh are pretty close, and no one using 9V snap cells is worried about high currents.. your metal detector is basically a specialized radio, not a surgy kind of thing. Also, NiCAD have a significant “memory effect” problem… if you don’t fully discharge them, they tend to lose capacity.
Most modern chargers for NiMh do handle NiCAD as well… older NiCAD chargers can be used to charge NiMh, but you can’t leave them on the charger unless it’s a trickle charger. The difference is that a NiCAD drops very slightly in voltage when fully charged, and NiCAD chargers use this to indicate “full”. NiMh cells just flatten out in voltage. The charging cycle, otherwise, is essentially the same.
The other common secondary cell is the Lithium type (Li-ion, Li-poly, etc). These need their own kind of charger… they need constant voltage charging at some levels, constant current at others. Lithium are the best energy density cells, but with a characteristic output of around 3.6V per cell, a 9V version would not be too practical.
NiMh cells typically last for 500 charge/discharge cycles or more. The standard definition of “last” means that they retain 80% or more of their original capacity over 500 charges… they don’t suddenly die, but they do lose capacity after awhile. Their aging, though, is almost entirely based on cycling them, so if this is a once-a-week recharge, they’re going to last you a long time.