I was recently caught out with a flat battery. I want to buy a jump battery to make sure it doesn't happen again. My car is a BMW 3 litre, 6 cylinder diesel that will need somewhere around 500-600 cranking amps. All the jump batteries I can find here have only 300 cranking amps. If I connect two of those batteries to my car at the same time, will that give me the 600 cranking amps I need?

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    Cant you use a battery-tender? Cheaper and your unused jump battery will probably go bad soon anyways. Or just get some jumper cables. Surely there is someone else with a car nearby should you need a jump-start once again? – Daniel Jan 30 '19 at 16:37
  • The car is a 4WD and I am often in the bush. – bpolky Jan 30 '19 at 16:51
  • Fit a second battery in the boot and use a split-charge system, then if you need to "help" the primary vehicle battery you can... – Solar Mike Jan 30 '19 at 16:54
  • I am looking for an answer to my question about connecting multiple jump batteries. Thank you. – bpolky Jan 30 '19 at 17:01
  • Well, I was hoping to offer you a sensible solution, at least, better use of your money than your idea of buying two jump batteries... But your money, your choice. – Solar Mike Jan 30 '19 at 17:10

you can. As long as you hook all positives together and all negatives together, the amperage stacks. DO NOT CONNECT RED TO BLACK OR YOU WILL EITHER EXPLODE A BATTERY OR FRY YOUR ELECTRONICS

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    and you have the space to make reliable connections... – Solar Mike Jan 30 '19 at 17:10
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    The amperage stacks in theory. In practice, the different resistance of the different battery hook-up connections means it won't stack very well at high currents. With 500A current, a resistance of 0.001 ohms will drop half a volt. – alephzero Jan 30 '19 at 17:51
  • i didn't want to get into electrical theory since it wasn't necessary. I won't claim my math is perfect, but e = 500 / .001 comes out to .17 volts. An alternator won't notice the difference. – John Lord Jan 31 '19 at 22:26

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