Batteries have changed in recent years. The old rechargeables we're familiar with are nickel cadmium cells, or NiCds. They served us well for long time, and still do. But they have a couple of so-called "problems. "
- They deliver about the same current and voltage as alkalines, but exhibit a sharp voltage drop-off when they get near depletion.
- They also do not have any more current capacity than alkalines, so rapid depletion devices like digital cameras drain them quickly.
- Finally, they have "memory." This means that if you fail to cycle them completely over time, from fully drained to full charge, they will begin taking only a partial current charges.
But balancing these "problems" is the fact that they are slow charge cells, so they don't build excessive heat as they replenish. They can also sit on the charger at full charge voltage without harm, due to a high internal impedance at charge.
But as good as the NiCd cell is, a new player has emerged in the rechargeable market. Todays preferred rechargeable is the nickle metal hydride, or NiMh, cell. These new NiMh cells deliver several times the current of the older NiCd's and are seen to advantage in digital cameras. These devices consume a lot of current, quickly as they operate and so these cells have become very popular in recent years. These new high-current capacity NiMh's also take a charge much faster than previous batteries, store more current as mentioned, and deliver it over a longer time at a consistent voltage.
There are a few downsides to them, too.
- They need a "smart charger," one that monitors charge current and can shut itself down to trickle once they are fully charged.
- They also get hotter than the NiCd's as they fast charge, and unregulated excess heat can damage them. Again, this is why they must monitor the current - heat lowers resistance in the cell, which causes current spikes to worsen and thus make more heat.
It's a wicked spiral effect.
- Third, they offer a lower voltage per cell, 1.2v vs. 1.5v for alkalines. And while "smart charger" prices have fallen these days, sometimes the lower voltage can be a show stopper.
For example, the average Garrett detector uses 8 AA's in series. With NiMh's @ 1.2 volts each, the total voltage yield is only 9.6V.
With alkalines or NiCd's, @ 1.5 v per cell, the total delivered circuit voltage is 12V.
Even in a 4-cell unit, like the Ace 250, four NiMh's only deliver 4.8v, compared to the 6v of alkalines.
That is a noticeable difference and depending on the unit, it may mean the detector wont work right. I've seen some reports about that. Remember most detectors now in existence were developed around alkaline batteries and eventually, NiCd's - before the surge in popularity of NiMh's. So unlike digicams, detectors are not high drain devices. They are intended to operate for long periods of time on a charge and so drain current from their power cells steadily and slowly.
SO even though the NiMh cell can theoretically deliver more current, the lowered voltage of NiMh's may cause your detector to work erratically or not at all. In that case, you will be forced to use alkalines or NiCd's.
There is no free ride and nothing is perfect. I'm an alkaline man, myself, although I'm going to give NiMh's a try this year. Their prices have come down drastically in recent times and they have advantages that can be useful - if they will work. It is almost crazy not to at least try them.
- They deliver about the same current and voltage as alkalines, but exhibit a sharp voltage drop-off when they get near depletion.
- They also do not have any more current capacity than alkalines, so rapid depletion devices like digital cameras drain them quickly.
- Finally, they have "memory." This means that if you fail to cycle them completely over time, from fully drained to full charge, they will begin taking only a partial current charges.
But balancing these "problems" is the fact that they are slow charge cells, so they don't build excessive heat as they replenish. They can also sit on the charger at full charge voltage without harm, due to a high internal impedance at charge.
But as good as the NiCd cell is, a new player has emerged in the rechargeable market. Todays preferred rechargeable is the nickle metal hydride, or NiMh, cell. These new NiMh cells deliver several times the current of the older NiCd's and are seen to advantage in digital cameras. These devices consume a lot of current, quickly as they operate and so these cells have become very popular in recent years. These new high-current capacity NiMh's also take a charge much faster than previous batteries, store more current as mentioned, and deliver it over a longer time at a consistent voltage.
There are a few downsides to them, too.
- They need a "smart charger," one that monitors charge current and can shut itself down to trickle once they are fully charged.
- They also get hotter than the NiCd's as they fast charge, and unregulated excess heat can damage them. Again, this is why they must monitor the current - heat lowers resistance in the cell, which causes current spikes to worsen and thus make more heat.
It's a wicked spiral effect.
- Third, they offer a lower voltage per cell, 1.2v vs. 1.5v for alkalines. And while "smart charger" prices have fallen these days, sometimes the lower voltage can be a show stopper.
For example, the average Garrett detector uses 8 AA's in series. With NiMh's @ 1.2 volts each, the total voltage yield is only 9.6V.
With alkalines or NiCd's, @ 1.5 v per cell, the total delivered circuit voltage is 12V.
Even in a 4-cell unit, like the Ace 250, four NiMh's only deliver 4.8v, compared to the 6v of alkalines.
That is a noticeable difference and depending on the unit, it may mean the detector wont work right. I've seen some reports about that. Remember most detectors now in existence were developed around alkaline batteries and eventually, NiCd's - before the surge in popularity of NiMh's. So unlike digicams, detectors are not high drain devices. They are intended to operate for long periods of time on a charge and so drain current from their power cells steadily and slowly.
SO even though the NiMh cell can theoretically deliver more current, the lowered voltage of NiMh's may cause your detector to work erratically or not at all. In that case, you will be forced to use alkalines or NiCd's.
There is no free ride and nothing is perfect. I'm an alkaline man, myself, although I'm going to give NiMh's a try this year. Their prices have come down drastically in recent times and they have advantages that can be useful - if they will work. It is almost crazy not to at least try them.
