Car Battery in the Trunk: How to Jump It and Get the Trunk Open
Published Wednesday, October 28, 2026 · Updated October 28, 2026, 5 PM ET · 5 min read · By Hassan, Owner of Roadmate Services
If your car battery is in the trunk, you jump it under the hood, not in the trunk. Most of these cars have a jump post under the hood, usually a red cap marked +. Jump there first. With power back, an electric trunk release that would not open usually works again, and you can reach the battery.
We had exactly this on Sunday, October 25, in an apartment parking garage in downtown Columbus. The car was a 2016 Hyundai Genesis, the battery was in the trunk, and the trunk would not open because the battery was dead.
Quick answer: a dead battery in the trunk
| Where to jump | The jump post under the hood, usually a red cap marked +, plus bare metal for the negative |
| Trunk won't open | Normal with a dead battery. Jump at the hood first, or use the hidden key or the inside release |
| Best tool | A portable jump pack, so no second car has to fit in a garage or tight spot |
| After the jump | Get the battery tested. A jump gets you going; it does not fix a weak battery |
| Call when | You can't find the jump post, the car only clicks, or you are on a highway shoulder |
What happened with the Genesis
A few weeks earlier, the same driver called us from downtown: he came out of the gym and the car would not start. We jump-started it. The battery was low, but he could not replace it right then, so he drove off on the jump.
About two to three weeks later he called back, and we met him in his apartment’s parking garage. On this car the battery sits in the trunk, and the trunk opens electrically. Dead battery, closed trunk. It is a neat little loop, and not the fun kind.
So I jumped the car first, through the jump terminals under the hood, with our portable jump pack. That gave the car enough power to open the trunk. Then I took out the old AGM battery and put in a DieHard Platinum H9 AGM with a 4-year warranty.
He left us a Google review afterwards: “Just completed battery replacement, was quick and efficient.” Thank you, Deshawn. The lesson from this one is simple: a jump gets you home, but a weak battery will be weak again.
Why is the battery in the trunk?
Carmakers move the battery to free up room in the engine bay and to balance the car’s weight, as Jalopnik explains. You find it in the trunk, under the trunk floor or under a seat on many BMW and Mercedes models, some Cadillacs, and sedans like the Genesis.
It is more common than people think. Interstate Batteries says more than a third of cars on the road in 2022 had the battery somewhere hard to reach. The engine bay got crowded, so the battery moved to the back, like a teenager claiming the basement.
How to jump a car with the battery in the trunk
On a highway shoulder, get safe, then call: hazards on, and stay buckled in or move well away from traffic. Do not open the hood next to moving lanes. The steps below are for a driveway, a lot or a garage.
- Open the hood and find the jump post. Interstate Batteries describes it as a remote terminal wired straight to the battery’s positive post, usually under a red cap marked +. Your owner’s manual shows it.
- Find a ground point: bare, unpainted metal on the engine or body, away from the jump post. Some cars have a marked negative post too.
- Turn off lights, radio and heat in the dead car. Keep the two cars from touching.
- Clamp red to the good battery’s positive, then red to the jump post. Clamp black to the good battery’s negative, then black to the ground point. With a jump pack, red to the post, black to ground.
- Start the good car or switch on the pack, wait a few minutes, then start the dead car.
- Remove the clamps in reverse order: black from the ground point first, red from the jump post last.
For some European cars that have only a positive post under the hood, Interstate suggests a portable jump starter rather than cables. Our full jump start guide covers the basics, and if the car still just clicks, read the signs your car battery is dying.
How to open the trunk when the battery is dead
If you need the trunk itself, these are the usual ways in, from SlashGear’s guide:
- Jump at the hood. Power back means the trunk button and the fob work again. With a trunk battery, this is usually the fastest way.
- The hidden key. Most fobs hold a metal key. Some trunks have a keyhole hidden under a cover or the badge.
- From inside. Fold the rear seats if they fold and reach for the glow-in-the-dark release handle in the trunk.
If one of these gets you in and the car starts, you may not need us today. Drive it, then have the battery tested soon.
Replacing a battery in the trunk
Many trunk batteries are AGM, like the one in the Genesis. Replace AGM with AGM; our post on AGM vs flooded batteries explains why. Some cars also need the new battery registered with the car’s computer.
If the same battery has needed two jumps in a few weeks, it is telling you something. Our guide to a car battery that keeps dying helps you rule out a drain before you buy a new one.
Battery in the trunk in Columbus? Here is how we help
A jump start in Columbus has an estimated range of $75 to $150. We use the jump posts under the hood and test the battery after the jump.
If the battery is bad, we can replace it on site, trunk and under-seat batteries included. We fit DieHard batteries, and the price is quoted by phone. See battery replacement in Columbus.
We work 6 AM to 8 PM daily, Eastern Time, and arrive in about 32 minutes on average, depending on traffic, weather and location. A garage is fine. So is a driveway.
Frequently asked questions
Why is my car battery in the trunk?
Carmakers move it to free space in the engine bay and to balance the car's weight, Jalopnik explains. BMW and Mercedes have done it for years, and so have sedans like the Hyundai Genesis. Interstate Batteries says more than a third of cars on the road in 2022 had a hard-to-reach battery.
How do you jump a car with the battery in the trunk?
Use the remote jump post under the hood, usually under a red cap marked with a plus sign. Clamp positive to that post and negative to bare, unpainted metal away from it. Your owner's manual shows the exact points.
How do I open my trunk if the battery is dead?
Try the metal key hidden in your fob, folding the rear seats to reach the glow-in-the-dark release inside the trunk, or jumping the car at the hood so the locks get power again. With a trunk battery, the jump at the hood is often the quickest way in.
Can I jump a trunk battery with a jump pack?
Yes, and it is often the better choice. A pack needs no second car parked nose to nose, which helps in a garage. Interstate Batteries suggests a portable jump starter for some European cars that have only a positive post under the hood.
Is a battery in the trunk harder to replace?
It takes a little longer: trim or the floor may have to come out, and many trunk batteries are AGM, which should be replaced with AGM. Some cars also need the new battery registered. It is still a normal job we do in driveways and garages.
The bottom line
A battery in the trunk is jumped under the hood, at the jump post. Jump first, and the trunk usually opens again. Then get the battery tested, because a jump is a start, not a fix.
Dead battery in Columbus?
Call (380) 288-2822, 6 AM to 8 PM daily, Eastern Time. A dispatcher confirms the price and an arrival estimate before anyone heads your way.
May your trunk open on the first press, and your battery never need a second jump.