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I have a Linksys router which I want to power with batteries so it can be a portable router.

The original power supply for the router is rated 12V DC 0.5A maximum.

I've tried powering the router with a 9V alkaline battery and weird things happened. I've expected it to be under powered, by that it won't even turn on or work, but what happened was the battery got hot and the router main chip got really hot.

Why did the chip and battery get hot? Will it work OK and not get hot if I add two 1.5V batteries and make a total of 12V?

What are the problems I may face when using batteries to power an electronic such as this?

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    \$\begingroup\$ Practically speaking, even if it worked it would not work long - to meet your goal, buy a router designed for battery power or at least one intended for USB power and get a portable USB supply. As for the failure, without internal details one can only guess, but possibilities include the battery being unable to meet a "hump" in current demand during part of a start up process, causing repeated high-energy attempts at that, to the chip somehow going into latch-up, etc. Some kind of switching supplies can even heat when used with lower than designed input, but probably not applicable here. \$\endgroup\$ Jan 7, 2017 at 22:54
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    \$\begingroup\$ Or perhaps even more likely, you connected the battery with the polarity reversed! \$\endgroup\$ Jan 7, 2017 at 22:55
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    \$\begingroup\$ Polarity wrong: Router is now fried. The small 9V akaline packages can only deliver about 100 mA current and nowhere near .5A that the router needs. A 12 V lead acid battery would have been better - if and only if the polarity is correct! \$\endgroup\$
    – Turbo J
    Jan 7, 2017 at 23:02

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I'd suggest your battery terminal voltage dropped, which would heat the battery due to it's internal resistance. There is no way of knowing exactly what happened in your router since we can't see the schematic.

There is no reason that using a 12 V battery (however, and with whatever cells you choose) won't work...BUT it has to be able to deliver the current needs of the router and have enough mA/h capacity to suit your expected runtime.

I'd measure the current into the router when active and using your AC power supply. Then you have some starting point to configure a battery solution.

Most AC plug pack equipment is tolerant of around 10% or so variation. It may be that you could use 9 * Alkaline C batteries (13.5 VDC for new batteries), but if you are really drawing anywhere near 500 mA then the runtime to 12 V (or some lower voltage, say 11.2 V) is likely to be only a 4-6 hours since you can only discharge the cells to about 1.2 V at best.

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    \$\begingroup\$ kioan.users.uth.gr/wireless/wrt54g/supply.html suggests your typical legacy linksys draws on the order of 5 watts across a fairly wide range of input voltages. Newer designs should do better, at least for the core components when lightly loaded by traffic less than 2 watts seems possible. A 9v "transistor" battery is probably less than 4 watt hours, but a 6-amp 12 gel cell should be good for ten times that or more. If the battery is to be re-used, discharge cutoff will be needed as the switching regulator could otherwise discharge it below recovery. \$\endgroup\$ Jan 8, 2017 at 0:18
  • \$\begingroup\$ Great link Chris. If the Op is using a WRT54G then the current draw and voltage charts provide lot's of help. \$\endgroup\$ Jan 8, 2017 at 0:32
  • \$\begingroup\$ holly crap, i have a linksys wrt54g so I am lucky. by what I understood is that the router can be run on a 5v, as the minimum volts required is 3.3v to power the router. \$\endgroup\$
    – Xios
    Jan 8, 2017 at 0:38
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Try three 18650 battery pack in series, that will give you 12V. Protect it with a battery management system (BMS) balancer so it doesn't overheat.

If you are trying to put it outdoors as a repeater, you can even add a small solar panel to charge up batteries and then from the batteries to power the router in a small protected box.

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    \$\begingroup\$ This does not answer the question, which was about why things overheated when powered with 9V battery. \$\endgroup\$
    – Justme
    Jan 30, 2022 at 19:35

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