How long do the batteries in the WM 08 Wireless Audio Module and the ML 80 headphones last? In other words, how many times can you re-charge them until they need to be replaced? Do they have batteries that can be replaced or do you simply have to buy totally new units? The WM 80 Wireless Audio Module is especially extremely expensive. You could literally purchase a low-end Vanquish for the cost of the WM 80 module. I hope someone out there has an answer for me. Thanks.