In brief, the answer depends on which Sienna you have. The gasoline-only 2017 Sienna uses a standard 12-volt lead-acid battery, while the Sienna Hybrid uses a high-voltage battery pack (typically nickel-metal hydride) as part of its hybrid system.
Here is a closer look at the two powertrains and the batteries they use, how they operate, and what to expect when replacing or servicing them.
Gasoline Sienna (non-hybrid) battery
The gasoline-powered 2017 Sienna relies on a conventional 12-volt lead-acid battery to start the engine and power the vehicle’s electronics when the engine isn’t running. It sits in the engine bay and is replaced much like any other non-hybrid car battery—by a repair shop or Toyota dealer—with typical lifespans of several years depending on climate and usage.
Sienna Hybrid battery
The 2017 Sienna Hybrid uses a high-voltage battery pack for propulsion, which is separate from the traditional 12-volt unit. That pack is usually nickel-metal hydride (NiMH) and is managed by the hybrid system. The 12-volt battery still exists to run accessories and control modules, but the high-voltage pack is not serviced in the same manner as a standard 12V battery and typically requires dealership or specialist service if it needs replacement.
Summary
For the 2017 Toyota Sienna, battery type depends on powertrain: a conventional 12-volt lead-acid battery for the gasoline model, and a high-voltage NiMH battery pack for the Hybrid. Always verify your exact trim and consult the owner's manual or a Toyota dealer for replacement procedures and safety considerations (especially with the hybrid's high-voltage system).