Initially, the small unit (which also doubles as a mike) needs to be charged for 2 or 3 hours but after that, charging from time to time seems effective and if you're really lucky and have a power outlet in your vehicle which doesn't make noise in your speakers when something is connected to it, then you can leave it on charge all the time.
Overall the BTAXS works as advertised and extremely well. I have no complaints about sound quality or connection issues etc. The problem with this product is with the logic.
The BTAXS doesn't seem to understand that you have turned your vehicle off or on. Previously I had a Kensignton LiquidAUX . When you started your vehicle, it connected with your phone and when you turned your vehicle off, it disconnected. Nothing else was required.
The BTAXS has to be manually connected each time you start your vehicle except in cases where you are 30 feet or so away (like in a garage next to your house) in which case it merrily keeps you connected to your phone until you are far away (and have forgotten) at which time it goes in standby mode (disconnects bluetoooth). Then when you come back to the vehicle, you think you are connected but your not. If you leave your vehicle close by, the BTAXS will be still connected to the car so if you get a call you first have to turn off Bluetooth before you can answer the call on your phone.
I don't believe anyone actually tested the thing for more than a few hours in which case it works extremely well, when it is charged and after connecting. But it's a high maintenance gadget, a first generation product so I would advise you to wait for the second generation.