These instructions apply to the Toyota Prius Mk1 Prius+ (ZVW40) 2012-2016.
For other models, please choose your vehicle here.
When the Smart Key on your Toyota Prius+ (ZVW40, 2012–2016) starts feeling unreliable — you have to stand right next to the car to lock or unlock, the tailgate only responds on the second or third press, or a “key battery low” message flashes up on the multi-information display — the cause is almost always the little coin cell inside the fob, not a fault with the car. The seven-seat Prius+ uses Toyota’s Smart Entry system, and because a keyless fob is constantly listening for the car it drains its battery faster than a plain button-only remote. The good news: the Prius+ key uses a CR2032 cell, it costs very little, and the swap takes a couple of minutes with one small tool. This guide walks you through it.
How to Tell the Fob Battery Is Dying
A coin cell fades gradually rather than dying all at once, so the warning signs build up over a week or two:
- Shrinking range — you used to lock the car from across the car park; now it only responds within a metre or two.
- A “key battery low” message on the dash display, which the Prius+ shows when the fob’s signal weakens.
- Smart Entry only works up close — you have to press the fob’s buttons rather than just walking up and touching the door handle.
- Intermittent response, worse in cold weather, because a tired lithium cell loses voltage further when it’s cold.
As a rough guide, a keyless Smart Key like the Prius+’s tends to need a fresh cell nearer once a year, whereas a plain button remote can go two to four years. If yours is a couple of years old and showing these symptoms, the battery is the first — and cheapest — thing to rule out.
The Battery You Need
The Prius+ Smart Key takes a single CR2032 — a 3 V lithium coin cell about 20 mm across and 3.2 mm thick, one of the most common cells sold anywhere. Buy a branded one (a good-quality lithium cell holds its voltage far better over time than a cheap multipack), and don’t substitute a thinner cell such as a CR2025 — it may seem to fit but won’t sit tightly against the contacts, giving you weak range straight away. If you’re ever unsure, the code is stamped on the flat face of the cell you remove; match that exactly.
What You Need
- One fresh CR2032 3 V lithium coin cell.
- A small flat-blade screwdriver (tape the tip to avoid marking the case).
- Clean, dry hands.
How to Replace the Prius+ Key Battery
- Slide out the mechanical (emergency) key: release the catch and pull the metal key from the fob.
- Insert the screwdriver into the slot the key leaves and gently separate the case halves — work slowly around the seam and don’t use excessive force.
- Note which way up the old cell sits before you disturb it, then lift out the old CR2032, avoiding touching the terminals with your fingers.
- Fit the new cell with the positive (+) side facing up, exactly as the old one sat, handling it by the edges.
- Click the case halves back together until the seam closes evenly, and slide the mechanical key back in.
- Test lock/unlock and Smart Entry from a normal distance.
⚠ Polarity matters. A coin cell fitted upside-down won’t power the fob and, in some holders, can bridge the contacts. Take a quick photo before you lift the old one out if you’re unsure — positive (+) side up is correct on the Prius+ key.
Did It Work?
Stand a few metres from the car and lock, then unlock, watching for the indicators to flash. Walk up and try Smart Entry by touching the door handle. If a “key battery low” message was showing, it usually clears on its own once the car sees a strong signal again — a short drive cycle guarantees it resets.
If a Fresh Cell Doesn’t Fix It
- Re-open the fob and double-check the cell is the right way up and seated fully.
- Confirm you fitted a CR2032 and not a thinner look-alike.
- Wipe the metal contacts with a dry cloth or a cotton bud — a fingerprint or a speck of corrosion is enough to cause weak range.
- If Smart Entry is dead, hold the fob flat against the START/STOP button and press to start on the backup transponder; the car will work normally while you sort the fob.
- If everything checks out and it’s still weak, don’t overlook the car’s own 12 V battery — a flat vehicle battery can mimic key faults.
New Key or Spare — Why It’s a Dealer Job
Changing the coin cell never disturbs the fob’s coding, so your key keeps working the instant the new battery is in. A brand-new or replacement key is different: it has to be matched to your car’s immobiliser and VIN with diagnostic equipment, which means Toyota or an auto locksmith. It’s worth keeping the battery in your spare key fresh too — a spare that’s sat in a drawer for two years is often flat exactly when you finally need it.
Frequently Asked Questions
What battery does the Prius+ key take?
A single CR2032 3 V lithium coin cell — a common, inexpensive battery sold in most supermarkets and hardware shops. Buy a branded lithium one and avoid thinner substitutes like the CR2025.
Which way up does the cell go?
Positive (+) side facing up, matching the cell you removed. If in doubt, photograph the old cell before lifting it out so you can copy its orientation exactly.
Do I need to reprogram the key after changing the battery?
No. Replacing the coin cell doesn’t affect the fob’s pairing with the car, so it works immediately. Reprogramming is only needed for a genuinely new or replacement key.
How long should a new key battery last?
Because the Prius+ Smart Key is a keyless fob that’s always listening for the car, expect roughly a year or so from a fresh cell — less than a plain button-only remote. If it fades much sooner, re-check the cell code and seating.
My key still won’t work with a fresh cell — now what?
Re-open it and check the cell orientation and that the contacts are clean and dry. If it’s still dead, the fob may have an internal fault and need replacing and coding by Toyota — and remember a flat 12 V car battery can look like a key problem too.
Will the car start if the key battery dies?
Yes. Hold the fob against the START/STOP button (Toyota marks the spot) and press to start using the backup transponder. The mechanical key hidden in the fob unlocks the driver’s door if central locking won’t respond.
To clear a service reminder after maintenance, see our Toyota Prius+ service indicator reset guide. For warning lights, look up the code on autodtcs.com.
Independent guide — not affiliated with Toyota. Always follow your official service manual and safety precautions. Read our full disclaimer.