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I have a 1991 Mazda MX-5 Miata with a dead battery in the trunk/boot. The car is currently parked between two other cars facing forward, so I cannot reach the battery terminals with my jumper cables.

If I remove said dead battery from the Miata and carry it over to a car I am currently borrowing, would it be possible to charge the dead battery with the jumper cables?

I am imagining there isn't some special magic about the battery being connected to the Miata during a jump, but I want to be sure because sulfuric acid is not something I want to be drenched in.

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  • The cars are side by side or in line? Why not just push the Miata out so you can R&R the battery or charge it?
    – Ben
    Jul 19, 2018 at 22:11

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You can do as you planned ie remove battery and connect to donor vehicle.

Then, start the donor vehicle and run it at about 2000rpm for 20 or 30 minutes with no lights, wipers heater etc - have the radio on for company.

This should, if you are lucky and the battery is not defective or completely flat, provide sufficient charge to start the other car.

Once the car is started, get it to a place to give it a good charge - a good run may be sufficient if the alternator is charging and you don’t need lights wipers heater etc.

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    In addition to that: your MX-5 has special terminals under the hood to use for jump starting. Please use these for your jumper cables because a lot of current will be used during starting, which otherwise might damage any electronic components along the way
    – MadMarky
    Jul 19, 2018 at 8:43
  • Another way to do it, would be to carry the full battery form the other car over to the Miata, jump-start it and then let it idle/drive it for a while to recharge.
    – Daniel
    Jul 19, 2018 at 10:36
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    @daniel, that does assume that the car with the flat battery starts easily - otherwise you could end up with two dead cars due to two now flat batteries and yes I have seen customers do that! So, I suggested that order of doing things for a reason...
    – Solar Mike
    Jul 19, 2018 at 10:40
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To answer the question directly, connecting two batteries in parallel will transfer some charge to the dead battery but it will be a slow and not very effective process. It could well take hours to transfer enough to crank the engine, so as others have suggested it would be better to start the engine using the good battery - this might well work using jump leads rather than swapping the batteries over.

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