2-cell Li-ion charger with USB input and 3 A ceiling
The Texas Instruments BQ25306RTER is a 2-cell Li-ion/polymer battery charger IC that takes a USB input and delivers a programmable charge current up to 3 A to a 9 V battery pack.
Charge current and cell count — the fit decision
The 3 A maximum charge current sets the charge-time floor for a 2-cell pack: a 2000 mAh 2S pack charges at roughly C/0.67, which is fast enough for most field tools but not a supercharger. The 9 V battery pack voltage confirms this is a 2-cell charger — a 1S pack at 4.2 V or a 3S pack at 12.6 V will not terminate correctly.
USB interface and programmable voltage
The USB interface means this charger can be powered from a standard 5 V USB port or a 5 V wall adapter. The programmable voltage feature lets you set the regulation voltage for the 2-cell pack, which is useful if your battery chemistry or cell balance requires a slightly different float voltage than the default. The constant-current charging mode is programmable via an external resistor, giving you control over the charge rate without firmware.
Surface-mount assembly is straightforward with a standard reflow profile for QFN packages.