I did something similar with a MEElectronics AF9-BK. Snagged the lipo out of a broken s9-hd pair i had, and went from 100ma to 180ma iirc. The device itself is tiny, 1.9 x 0.4 x 0.4 and something like 10g.

You couldn't stuff a bigger battery than a s9-hd 180ma lipo in it i think, its pretty tight after the mod. But, i went from 6hr battery life, to around 10 hours.

Build quality and sound quality is pretty decent, for the price. And i got it ~1/2 current retail on sale at newegg, so i'm pretty happy with the device. Only gripe is no charge/usage at the same time. I'd love to make a mini battery pack with a 500ma lipo and small 5v dc/dc converter to charge it on the go, but its still limited as far as taking 4-5hrs to charge from a full dead, and no playback during charging.

Still, if you can get it under $40, i'd say go for it.

And btw, if you do mod a new battery in, don't solder the lipo leads off the board. I was too yellow to get a soldering iron near those joints, considering one slip would be a dead short to an unprotected lipo. Just cut the leads one at a time, and then solder/heatshrink the leads from your s9-hd/whatever battery you use instead.

I bought the Plantronics Backbeat Go, & I'm very pleased with it.



After the frame on the Nokia BH-505 snapped, I got a Samsung HS-3000 bluetooth clip & used it connected to the wired headphones. That worked OK, but still was sort of wire-y tangly and fumbly putting the pieces together, but the sound was good for bluetoothed mp3's & worked OK after you assembled & set up.

I got the Backbeat Go to reduce all that wire-y setup plugin stage, & it's great. It also takes calls & has a microphone. I listen to sort of 50/50 classical & pop music, & find that sound quality is a little compressed & flat sounding for very busy material, likely as a bluetooth data skimping artifact. Bare stuff like string quartets are really good - open, lots of dynamics, good frequency response - but for more wall-of-sound popular music it gets sort of flat. Still, not bad, & OK for casual listening.

The ear buds stay in surprisingly well if you use the optional stabilizer things. I use headphones with both earpieces in when I want isolation in a noisy room, but use just one earpiece if I'm walking around so that I don't get isolated from events in the environment & get run over by a truck or something. I thought these would need a little clip or something to the collar to keep from falling off if just one earpiece was in, but they stay put anchored by one earpiece & the other side dropped over the shoulder. I'd think that with both in & the stabilizers used, they'd stay on well enough for running; they're certainly fine for the bike.

Short note: I'm very satisfied with them. I have no complaints, & can't think of more I'd want from them. It looks like they're marked down as low as $54 here & there.

Edit: By the way, the Backbeat Go charges via the same USB connector as the N900, so no need for more wall warts lying around, you can use it on the N900's charger, & even charge it in the car on the car charger. I like that, less junk everywhere.

On an unrelated note, I wish I'd kept the BH-505 carcass after it broke, to scavenge the BT module. There are a lot of fun projects out there using scavenged BT modules, like proximity-activated power strips, etc.