9-V rechargeables are not quite like our familiar AA, AAA, C or D rechargeables- which are usually rated at 1.2 volts, whether nickel metal hydride or Nicads. To get the higher voltage in the "9" volt rechargeable, the maker basically wires a series of teeny-tiny individual 1.2 v batteries in series and puts the package in a shell the size of a 9-V battery, making the 9-V rechargeable sort of a "battery pack". Most of the manufacturers cheat a bit and only use 6 or 7 cells in it- resulting in a 7.2 or 8.4 volt battery, not really 9. This will work reasonably well in many applications that are designed for a 9-V alkaline battery. If you read the labels on these "light" rechargeable batteries they say they are for "9-volt applications". It has been several years (pre Minelab) since I used these batteries in a detector, and they worked, but had a rather short life of maybe 3 or 4 hours. However, there are a few manufacturers such as VARTA that pack 8 cells into their 9-V rechargeable, making it really a 9.6 volt battery. I used these in the past and they last much longer in a detector before needing recharge. Many chargers can take 9-V batteries in them, and would certainly fully recharge the 7.2 or 8.4 V versions, but I wonder if they can fully charge the 9.6 volt ones--- in any event, I would certainly look for these for probes or detectors and read the battery labels very carefully to see their true charged voltage (they should say). Again, this is info from several years ago, so things may have changed.
