My goal is to use my laptop, a pioneer dj controller and 2 krk rokit 5's (50W class-AB amplifier boxes) for a party all at the same time for about 6-8 hours in a place without access to grid power.

For this I would probably use one or two 12V batteries with the needed Amp h.

  • Can I keep track how much the batteries have been used?
  • if no: is it possible/safe to fully use them, i.e. fully discharge them?
  • \$\begingroup\$ yes, it's possible to monitor batteries, no, it's not safe to fully discharge 12 V (that probably means lead-acid) batteries, in general. However, that will be stated on the datasheet of the batteries. \$\endgroup\$ May 19, 2019 at 13:55
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    \$\begingroup\$ Also, think about what you want. That's ca 200W in speaker power alone. You can basically forget about your laptop at that point. 8 hours of 200 W = 1.6 kWh. Assuming 100% step-up efficiency (realistically, for dynamic loads, assume 50%), that means you need to get 1.6 kWh out of 12 V, meaning that you need more than 1.2 kAh. In words: More than a kiloamperehour. Compare that to what your batteries advertise. Really large car batteries offer something like 100 Ah. So, you'd need more than 12 of really large car batteries. Do you spot the problem with that? \$\endgroup\$ May 19, 2019 at 14:02
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    \$\begingroup\$ I suggested that you find out the power needs to your previous question, so how do you know you need 1 or 2 batteries? And what size batteries are you considering? \$\endgroup\$
    – Solar Mike
    May 19, 2019 at 14:28
  • \$\begingroup\$ don't use class AB amplifiers in a portable power applications, use class D \$\endgroup\$
    – Neil_UK
    May 19, 2019 at 15:38
  • \$\begingroup\$ I do spot the problem with that. i came to believe this could work because i had seen another post link and here it said a 12v 20ah battery would be more than enough to power the same monitors i have for an hour. im sorry if im raising funny or annoyed faces but im not native english and i really am a beginner when it comes to this electronics tech stuff. \$\endgroup\$
    – fh teun
    May 19, 2019 at 18:48

1 Answer 1


first, you arent going to do this with 'one or two' car batteries. you arent going to be able to do this with one or two deep cycle marine batteries. MAYBE with 'one or two' industurial forklift batteries, but they weigh around 3 tons and run upwards of $10K. but for the sake of posterity ill pretend that you do. lead-acid batteries can be monitered with a battery management system, or you can get a crude idea by checking their voltage with a multimeter, page 5 of this pdf has more detail, but the short version is that if you plan to use the batteries again, you dont want to let them drop below 11.5v at the terminal.

just rent/buy a generator

  • \$\begingroup\$ thanks for the reply. im still a bit shocked my monitors need batteries that weigh 3 tons. do they take up that much at home too? anyway. what generator would be able to suffice here? would this be enough or would i need a bigger one? google.com/… \$\endgroup\$
    – fh teun
    May 19, 2019 at 20:55
  • \$\begingroup\$ they dont need to weigh 3 tons, unless you need them to last 8 hours. you could absoloutely hook them up to your car battery and get full volume, no problem... for maybe 10 minutes. youd have to do the math to see what kind of wattage you system is going to max out at, and have whatever source rated AT LEAST that much, preferably more or it might struggle. the generator you linked is rated 750 watts/3.6 amps as its peak, meaning it will NOT sustain that output for more than a few seconds. my vacuum cleaner is rated for 12 amps... \$\endgroup\$ May 22, 2019 at 15:57
  • \$\begingroup\$ it is because i saw this link that i thought it would be possible. here someone explains how a relatively small battery would be able to power both speakers for at least 1 hour (russel mcmahon's comment). so does this mean his calculations are incorrect? \$\endgroup\$
    – fh teun
    May 22, 2019 at 19:06
  • \$\begingroup\$ and what kind of watts/amps would i need within the generator? \$\endgroup\$
    – fh teun
    May 22, 2019 at 19:49
  • \$\begingroup\$ its one of those things that MIGHT be possible, but its like hooking up a horse trailer to a prius. it might pull it, it might cut out halfway up a hill. the thread you linked mathed that he might be able to get a max of 1 hour with his setup, which was half of yours, and ultimately suggested an inverter, which can be hooked up while the car is running (effectively turning it into a generator). you need to do the math for what your setup will max at, then get something bigger than that \$\endgroup\$ May 28, 2019 at 17:51

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