Like its Bose and Jawbone competitors, this model has a built-in rechargeable lithium ion battery. It provides up to six hours of continuous playback, though you can do better than that if you play your music at lower volumes.
The SRS-BTX500 has a 2 x 10W power rating, which adds up to 20W of total power. For a small speaker, it's got some kick to it and can fill a small to medium-size room with sound.
What I liked most about it is that it sounds very clean for a Bluetooth speaker and the punchy bass holds together pretty well at higher volumes. That said, the bass isn't huge, and I did get some distortion when I cranked up the volume on bass-heavy tracks such as Swedish House Mafia's "Greyhound." It sounded fine up till about 75 percent volume (call it 8 out of 10), then got a little crunchy when I pushed it past that point. In other words, the speaker does have its limitations and you're going to get your best results with the volume in the 40-to-60 percent range.
As noted, there's a sound mode button on the side of the speaker with a little LED light next to it. The default setting is for Mega Bass (amber LED), which is supposed to help deliver "high-quality bass." Tap it once and it shifts to a green LED and Mega Bass + Surround, which opens up the sound stage a bit with some digital processing. Tap it again and the sound effects are turned off. After playing around with sound button a bit, I leaned toward the default Mega Bass setting.
I compared the SRS-BTX500 with the Bose SoundLink Bluetooth Mobile Speaker II, which I like a lot and offers similar battery life (6 hours is OK but not great; the Jawbone Big Jambox is the winner there, with up to 15 hours of continuous play). The Bose also plays impressively loud for its size, but I thought the Sony sounded a little bit clearer and was a bit better overall. But it is a larger speaker, so you'd hope it would deliver better sound.
If you're considering the $199.99 SRS-BTX300, that model also is a very good performer for its size, but the BTX500 is a noticeable step up in sound quality. I personally would pay the extra dough for the BTX500.
As for speakerphone performance, it was decent, though not great; the Big Jawbone offers better speakerphone performance. Callers said I sounded slightly muffled, though my voice did get clearer if I moved closer to the speaker, which was about two feet away. I could hear callers fine.
The Bose SoundLink Bluetooth Mobile Speaker II and its predecessor have really owned the premium portable Bluetooth speaker market (yes, the Jawbone Big Jambox is a strong product, but it hasn't had nearly the success of the much smaller, original Jambox). While the SoundLink II is an excellent product, its dominance has been more than partially fueled by Bose's massive marketing efforts.
The Sony SRS-BTX500 won't get that kind of support from Sony, but it certainly holds its own against the Bose. It's a slick, excellent-sounding portable Bluetooth speaker that also features speakerphone capabilities (the Bose doesn't offer that), a USB charging option for smartphones, and NFC pairing for NFC-enabled devices. As I said in the beginning of this review, if you're in the market for a premium portable Bluetooth speaker, the SRS-BTX500 should certainly make your short list.