The belts have been upgraded from 10 to 25 charges for a while now. I have one on me at all times for those synths in Jeuno where the materials cost a fortune or those that are just too high for me to reach yet.
There is no way to recharge this item, after you get to 0/25 you need to drop it and buy a new one. Bad deal you think? Let me do some calculations with numbers based on my server and experience:
-> 10k GP x about 10 gil/GP = 100k gil for this belt (and some work handing in gp items).
-> 100k / 25 charges = 4k per charge.
4k for a better chance not to lose a 700k elemental ore on a synth is a good deal if you ask me. But it gets better: you need to keep in mind that the charge lasts you about 3 minutes, so you can do several synths with one charge of this belt. If you do 4 700k synths during that time you only pay 1k more for each synth to get less chance of faillure. And if you hurry up you can do more then 4 synths.
If that doesn't convince you, here's another approach. If those 25 charges and possible 100+ synths give you only 1 time where you don't break your elemental ore where it would have broken without the belt... then that has saved you 700k, 7 times the price you paid for this belt.
Conclusion: this is a great item, not just the goldsmithing one but the other crafts as well, i recommend it to anyone working with expensive materials.