im working on a project with arduino, led matrix and accelerometer, it should be autonomous , so the use of a battery is mandatory. Also it should be rechargeable so i ask you guys wich is the best solution.
I suppose Li-ion batteries is a correct choice
How is it to recharge the batteries through the usb interface? Do we need a recharging circuit ? how much voltage should it give to feed arduino +the matrix+the accelerometer?
Lithium batteries are particularly intolerant of incorrect charging; simply connecting the battery to USB would be a good way to generate a fire or explosion (no, I am not kidding).
Since Li technology batteries are ~3.6V, you need either a 3.3V arduino variant with an LDO regulator, 2 cells, or a boost regulator.
There are ICs available specifically designed to charge Li cells from USB voltages (MAX1555, etc).
In addition Li batteries have to be protected from over discharge to prevent permanent damage, so some kind of low voltage cutoff/turn off is required.
Unless you really require the higher power density ( you also pay for this increased density) you are probably better off with other less fussy types of rechargeable batteries.