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I am planning on to design a system to power my router. Unfortunately, there are shortcomings of electricity in our area and I want my router to operate 24/7. I have read the specs of the router and it requires 12v/1A | 12watts.

What I want to do now is to select a Small size rechargeable battery so that I can power my router through it when my main electric power is cut-off. I thought about 3v7 LI-ION battery with a Boost converter but LI-ION can't provide me, ideally about 3.4A (12w/3v7) continuously. So should I connect two LI-ION in series (3.7x2) to drive Boost converter i.e (12/7v4 = 1.62A) or there is another better approach which can be both cost-efficient and suitable for the above purpose?

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    \$\begingroup\$ The first step is to figure out how many Watt hours (Wh) you need. If you want to keep the router alive for 10 hours, then you need 10 hours * 12 Watts / 80% efficiency = 150 Wh. This would not be a "small size rechargeable battery." So how long DO you want to keep it alive for? \$\endgroup\$ – mkeith Mar 1 '17 at 7:33
  • \$\begingroup\$ @mkeith: Thanks for the reply, i forgot to mention that one. I need at least 52Wh. It should be alive for 3.5 hours. \$\endgroup\$ – Nouman Tajik Mar 1 '17 at 8:29
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    \$\begingroup\$ If you only need 12V DC I'd be inclined to go for the simpler option and use a 12V sealed lead acid battery rather than requiring a boost converter - then you won't lose any power in the converter. And while the router spec might say that it requires a 12V 1A supply you will probably find that it actually takes less power most of the time so you can get away with a smaller battery than you think. \$\endgroup\$ – Finbarr Mar 1 '17 at 10:46
  • \$\begingroup\$ For stationary batteries where weight is not an issue, lead acid will be cheaper and much easier to use than Lithium. \$\endgroup\$ – bobflux Mar 1 '17 at 10:52
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    \$\begingroup\$ Lithium ion will produce a more compact solution compared to lead acid. But lead acid is much cheaper than Lithium ion on a cost per Wh basis. Each 18650 cell (cylindrical laptop cell) is roughly 9 Wh, depending on specific cell. You could use 6 in series plus a buck converter. Or you could use a small lead acid battery. Due to shortcomings of lead acid, I would suggest using 100 Wh if you go that route. 100 Wh /12V = 8Ah, approximately. So an 8 Ah 12V lead battery. This would not be a large battery. \$\endgroup\$ – mkeith Mar 1 '17 at 16:08
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A small uninterruptable power supply can be made with a motorcycle or automotive (or even a gel cell) 12V battery that will suit this need. PicoUPS at Amazon.comPicoUPS. The changeover when power fails is automatic, as is the recovery when power returns.

More elaborate uninterruptible power supplies would also deliver AC for other items (a telephone answering machine, for instance) while delivering AC through the wall-wart to operate your router.

If you can get a power meter (Kill-a-Watt for instance), you may be surprised to find that your router's nameplate power requirement is very conservative: it might only take a fraction of the 12W that the adapter provides. For this use, the 'V-A' reading tells what the drain on a battery would be.

A battery alone will not handle the switchover, and will require charge control, and won't give regulated output for your 12V appliance. It might work, but isn't ideal.

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