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I have connected a 3.7v-4000mah battery to a load via a voltage booster MT3608 (3.7V to 12V) . load current is 100ma. how long does battery can work?

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For this you will need to consider your batter capacity in watt-hours. So for your 3.7V 4000mAh battery, plugging into the equation mAh * V / 1000 = Wh, you get 4000mAh * 3.7V / 1000 = 14.8Wh. Now we can convert it back using 12V for our V value in the equation and get (14.8Wh * 1000) / 12V = 1233.33mAh. And with a 100mAh load that would be approximately 12.33 hours of runtime with an ideal DC/DC converter. However, you'll likely have a roughly 90% efficiency and therefore see only 12.33 * .9 = 11.09 hours of actual run time (thank you MatsK for reminding me that practicality is nearly never ideal).

I have a feeling I forgot something so others shall feel free to correct me or point out errors. I'm writing this on mobile so can't currently format it, maybe later.

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  • \$\begingroup\$ The efficiency of the DC/DC converter. If it is a 90% efficiency then you have to take away 10% from the time. And you have also take in consideration the discharge curve, example: cdn.sparkfun.com/assets/6/7/4/7/9/5112a224ce395fb479000003.png \$\endgroup\$ – MatsK Sep 12 '17 at 4:20
  • \$\begingroup\$ Will also need to take into consideration the switching current \$\endgroup\$ – MCG Sep 12 '17 at 7:11
  • \$\begingroup\$ @MatsK does battery volage drop just after about 9 min?its confusing me \$\endgroup\$ – amin Sep 12 '17 at 9:01
  • \$\begingroup\$ I have no idea where 9minutes is coming from? The battery voltage will start to drop as soon as you connect a load to it. The discharge graph can be like this for a LiPo battery: i.stack.imgur.com/LV91V.gif \$\endgroup\$ – MatsK Sep 12 '17 at 10:10
  • \$\begingroup\$ Possibly faulty battery or converter \$\endgroup\$ – Bakna Sep 12 '17 at 10:19

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