I've been happily using a Yamaha VA10 to amplify my harmonica for years. It isn't rechargeable but the batteries last for ages and you can run it from the mains. It gives out an alleged 6 watts (who am I to argue) and is loud enough to get me heard even in a fairly noisy pub environment and is great for outdoors. It has treble, middle and bass controls and there is a variable delay that takes the dryness off your sound if you want it (Gain and chorus controls too if you want them). I can get a pretty clean sound at good volume from it, which is what I want. They look a bit like one of those big old radio sets and have a nice leather carry-handle, weighing in at around 10lb I suppose.   I don't know whether they're still available so you may have to look for them on eBay, etc. I paid £100 new for mine in 2002.