Volts are just the push behind the current. What runs your detector is the watts, that is the total that is needed. Watts are volts times amps. Metal detectors are designed to regulate the voltage from your power source. Most are designed to warn you when the volts are no longer able to deliver the watts needed with alkaline batteries. They are also designed to regulate the volts so that low voltage in the batteries do not affect performance. As such, they run on voltage less than 1.5 volts per battery.
Voltage regulation can both reduce voltage and increase it. A taser battery does not contain 10,000 volts. A 110 volt AC circuit can charge 1.5 volt batteries. If the AC voltage drops to 100 volts, they can still charge the batteries. There is a device for charging my 5 volt batteries in theDeus coil, remote, et al, that uses a 1.5 volt battery. Rechargeable batteries can deliver the watts needed just fine.
As a matter of fact, my Pentax digital camera manual warned against alkaline batteries saying that they could be used to set up the camera but would not support all the functions. Their recommendation was rechargeable batteries or the lithium ones. The older generation rechargeables (non LSD) batteries lost their charge rather quickly and that could be a problem if you forgot to charge them. I know because I would charge two sets for my camera, install one and when the ones in the camera needed replaced, would find the replacements charged at the same time were also out of "juice". The newer rechargeable batteries do not lose their charge at nearly the same rate, they seem to me to be comparable to alkaline in this respect.
If you do an internet search on rechargeable batteries, you will see that rechargeables can deliver the watts needed at lower voltage than possible with alkaline batteries, the reason for the Pentax recommendations. Plus 8 rechargeable batteries can be charged for 3/10 of a penny. I've seen it touted by alkaline fanatics that they can pay for their batteries with their finds. I can pay to recharge 6 times with one penny as I only use 4 batteries plus they last as long as alkaline ones.
It is up to you, you can do whatever you want but I have used rechargeable batteries for years. I have replaced the old non LSD one with newer eneloops and have had not problems other than when I don't watch the charge meter, the rechargeables can go dead immediately. I have laid down my detector after a find, and it was acting perfectly normal, and when I picked it up, it was dead, similar to lithium power tools. Another thing is that most detector's battery level indicators are designed for alkaline batteries. Rechargeable ones show lower voltage when installed but still have all the power available needed to run your detector.
I use envelop white and black and Energizer LSD batteries and a La Crosse charger which can tell me how many amp-hours they contain, can drain and recharge, can keep draining and recharging until the batteries reach maximum amp-hours, and can charge batteries a different rates. I am sure it didn't take long to pay for themselves and will keep on paying long afterwards. Sorry for the long reply.
