- If you drive a full or plug-in hybrid, it is better not to jump start another car with it.
- The 12V battery of that kind of hybrid is small and only feeds the electronics. It is not built to pull a starter motor.
- Toyota states at the jump start point that you may not start another car with it. Other brands often write the same, but not all of them. Your own owner's manual is what counts.
- With jumper cables the current runs straight from your hybrid. That is exactly the situation you want to avoid.
- A mild hybrid (48V) is different: it usually still has an ordinary 12V starter motor. There too, the manual decides what is allowed.
- The other way round is fine: you can simply jump start a hybrid with a flat 12V battery yourself.
You are in the car park and someone next to you cannot get their car started. You drive a hybrid, so you think: just hook up the cables. With a full or plug-in hybrid that is almost always a bad idea, and not because your hybrid would be too weak. It comes down to something else.
In short: a hybrid has two batteries. The large high voltage battery drives the car and is fully shielded. The small 12V battery only runs the on-board electronics, the lights and the starting system. You can only reach that second one, and it is not built to start another car.
Why a hybrid is not a good donor
An ordinary petrol or diesel car has a battery designed to feed a starter motor. That takes a few hundred amps, short and heavy. That is exactly why it carries a CCA value: the cold start current (Cold Cranking Amps) the battery can deliver at low temperature.
A full hybrid and a plug-in hybrid do not have that heavy starter motor. The combustion engine is cranked by the electric motor, fed from the high voltage battery. The 12V battery therefore never has to deliver a large current burst and is built correspondingly light, often around 35 to 45 Ah. It is topped up by a DC to DC converter, not by an alternator.
If you connect a car with a flat battery to it, that starter motor draws current the system has never had to deliver. In the best case a fuse blows. In the worst case you damage the converter, and that is not a cheap repair.
With jumper cables: exactly the situation you want to avoid
The question often comes back as "can I start a petrol car with jumper cables from my hybrid". The answer is the same, and the reason actually becomes clearer with cables involved. Jumper cables connect the two cars directly to each other. The current the other starter motor needs then comes from your 12V system. That is exactly the load that system is not built for.
A jump starter works differently. It has its own battery on board and delivers the current itself. Your hybrid is not involved at all, not even if you have the jump starter lying in your own boot. That is the difference that matters: not the brand of cables, but where the current comes from.
A mild hybrid is a different story
Note the difference with a mild hybrid, often labelled 48V mild hybrid or MHEV. Besides the starter generator it usually still has an ordinary 12V starter motor for the cold start, and therefore also a heavier 12V battery. Technically that car is closer to an ordinary petrol car than to a full hybrid in this respect. Whether you may give a jump start with it differs per brand and model. There too: your owner's manual decides, not the rule of thumb.
Note: this is general information, not a replacement for your owner's manual. Always check the jump start chapter of your own car first, because that is what counts. Toyota, for example, states at the jump start point that you may not start another car with it. Many other brands do the same, but it is not described the same way for every brand and every model. If something breaks while your manual advises against it, that damage is usually not covered by the warranty. Not sure? Call your brand dealer, it only takes two minutes.
The other way round is fine: jump starting a hybrid
Do not confuse this with the reverse situation. If your hybrid itself will not start because the 12V battery is flat, you can simply give it a jump start. That is a normal action and it is also described in the manual.
On many hybrids the 12V battery is not in the engine bay but under the boot floor or behind a side panel. That is why there is a designated jump start point under the bonnet, usually a red cap on the fuse box. You connect the red clamp there, and the black one to a bare earth point. Check your manual for the exact location of that point on your model.
Looking for which jump starter suits your hybrid, with the CCA value per model? That is covered in jump starter for a hybrid car. This article is about whether you may help someone else.
A jump starter solves both of these. You do not need a second car and you do not put a load on anyone's electronics. View the jump starters
What to do instead
If you want to be able to help someone else, take a jump starter with you instead of jumper cables. It delivers the current itself, so your own car stays completely out of it. That also works if there is no one else in the car park.
Which model you need depends on the car you want to start, not on your own hybrid. Check the CCA value on that car's battery label and choose a jump starter that at least matches it.
| Car you want to start | Suitable up to | Model |
|---|---|---|
| Small petrol, city car | 480 CCA | Boost Air Micro |
| Mid-size petrol, small diesel | 620 CCA | Boost Mini 3750 |
| Diesel, SUV, start-stop with AGM battery | 960 CCA | Boost Pro 8250most chosen |
If in doubt, pick the model above. A jump starter that can handle more than needed does no harm, the other way round you are still stuck. You can read what those numbers actually mean in what CCA is and why it determines your choice.
Frequently asked questions
Can you jump start another car with a hybrid car?
With a full or plug-in hybrid it is better not to. The 12V battery is small and is fed by a converter that is not built for that current burst. Toyota states at the jump start point that you may not start another car with it, and more brands do the same. Check your own owner's manual, that is what counts.
Can you start a petrol car with jumper cables from a hybrid?
That is the same action and the same warning. With jumper cables the current comes straight from your hybrid's 12V battery, and that is exactly the load that system is not built for. If you still want to be able to help someone, use a jump starter with its own battery instead. Your own car then stays out of it.
Does this also apply to a mild hybrid?
Not in the same way. A mild hybrid (48V) usually still has an ordinary 12V starter motor and a heavier 12V battery, and is closer to a petrol car in this respect. Whether giving a jump start is allowed differs per brand and model. Check it in your owner's manual.
What breaks if I do it anyway?
Usually a fuse, and then you are lucky. More annoying is damage to the DC to DC converter that charges the 12V battery. That repair quickly costs hundreds of euros and is usually not covered by the warranty if your manual advises against it.
Can you jump start a hybrid itself?
Yes, that is a normal action. Use the designated jump start point under the bonnet, often a red cap on the fuse box, and not the battery terminals at the back. The exact location is in your owner's manual.
Does this also apply to a plug-in hybrid and an electric car?
Yes. A plug-in hybrid and a fully electric car also have a separate 12V battery without a heavy starter motor attached. You cannot use it to give another car a jump start. Here too: check your owner's manual.
Which jump starter do I take if I want to be able to help others?
Choose based on the car you want to start, not on your own hybrid. For most passenger cars the Boost Pro 8250 is more than enough, since it is suitable up to 960 CCA.
