|I read in an article about batteries about a Reverse Coulomb Counter. What is it?
Although I've never heard of such a device myself, I can guess what it means. A coulomb is a standard unit of electric charge. Since a battery is a pump for electric charge, measuring the number of coulombs that have flowed through a battery is a way to determine what fraction of that battery's storage capacity has been used. (It's analogous to measuring how many grams of sand have flowed through the neck of an egg timer or how many liters of water have flowed out of a water tower.) When a battery is being recharged, measuring the number of coulombs that have flowed in the reverse direction through the battery is a way to determine how much recharging has occurred. Thus, I suspect that a "reverse coulomb counter" is a device that monitors the flow of charge backward through a battery as it is being recharged. This backward flow of charge should be almost exactly proportional to the extent of recharging.