If your Tesla’s 12-volt battery dies, the touchscreen goes dark, the door handles won’t present, and you can’t get in — even if the traction battery still shows 60 percent range. That’s because a Tesla runs two separate battery systems, and the small 12-volt battery, not the large lithium-ion pack, controls the locks, the computer, and the accessories (Capital One). A portable jump starter kept in the frunk means you’re not waiting on a tow truck when it happens.
Why this happens even to newer Teslas
The 12-volt battery runs constantly in the background, powering sensors, the infotainment system, and the electronics that unlock the doors, and it can drain even while the car is parked and plugged in — leaving you locked out with no way to open the doors normally (Capital One). On Model 3 and Model Y, recovering it means connecting an external power supply to jump points near the front tow hook, behind a small access panel, then waiting roughly ten minutes for the car’s systems to reboot before the doors and screen come back (Capital One).
What to buy
Skip the bulky lead-acid jump box from the trunk of an old gas car and buy a compact lithium jump starter instead — it’s small enough to live in the frunk permanently and won’t take up meaningful cargo space. The NOCO Boost Plus GB40 is a common choice: a 2.4-pound lithium pack rated for 1,000 peak amps, enough to start gas engines up to 6.0 liters or diesels up to 3.0 liters, with an IP65-rated case and reverse-polarity protection. NOCO lists it at $99.95 as of August 2026 (NOCO); jump-starter prices move around with sales, so check current pricing before you buy. It also works as a USB power bank and flashlight, which is useful if you’re stuck after dark.
Where to keep it
Store it in the frunk rather than the trunk — that’s where the jump points are, and you don’t want to be digging through cargo in the dark to find it. Check it every few months. Lithium packs hold a charge far longer than lead-acid jump boxes, but they still self-discharge slowly, and you don’t want to find out it’s flat at the same time your car’s 12-volt battery is.
Photo by Julia Avamotive.