Digital equipment use signals that are square waves. This means the trailing edge of the wave goes from some level (often 5 volts) to zero in theoretically no time. This creates a theoretically infinite frequency bandwidth. In actuality, inductance within the electrical circuits limit that range. In layman's terms, all digital equipment has the potential of causing electrical noise. This can be in the wiring and transmitted over the air. That's why if you look at equipment data plates in the US you will see a statement that it complies with FCC regulations. Having said all that: it's no surprise that you would get some interference.
There are a few ways to eliminate it. First, as someone suggested determine if it's radiated noise or from the power. If it doesn't go away when the antenna is disconnected, the issue is likely coming from the power system. If that's the case, put a filter on the power system. It may be as simple as running the VHF and stereo power through a toroidal core (google it.) This is easy and cheap and you can get them out of old junk computer power supplies. Just loop the power wire in a few turns just like it was in that old power supply.
If the noise is radiated (goes away when the antenna is disconnected), I'd be really careful to look for a bad ground. Look particularly around the charger and battery grounds. This includes any temperature monitoring as well as voltage sensing wiring which goes to the batteries. You may need to disconnect those grounds and clean them to ensure they aren't corroded between mating surfaces. If all else fails, you may need to replace the battery charger. If it were me, and I only rarely used it, after I checked all the grounds, I'd most likely turn off the VHF and stereo when charging then ignore it unless it's bothering the neighbors.
Ken
