Buy 3 x 18650 batteries, a 3s 18650 10A BMS, a DC male power plug, a DC female power socket and solder them. Power up using a 12V 2A (or higher ampere) power adapter. You are done!


Some of you should be working from home and are looking for power backups to survive your “day job”. With the extended power cuts, the need for power backups has definitely gone up.

I’ve been encouraging my colleagues on router power backups for a long time. Some of them got some actions and some did not. However, I thought of compiling some info about how to get around this.

What made me interested to look for a power backup for the router first was to keep the meetings uninterrupted due to the very short power outages, where the router switches off and switch on again within seconds. For that, I got a small power backup device which I’ll mention later and it could survive my fiber router for 5+ hours (if the connected phone doesn’t ring, yes).

I’ll be focusing on router power backups mainly in this post. If you wish to learn about how you can get a battery-powered power backup with/without solar power, “DIY Off Grid Sri Lanka group” FB group has a large number of resources.

I’ll first discuss how you can create a power backup yourself and later some other solutions as well.

Do it yourself: A simple power backup for the router

There were enough providers earlier where we could buy power backups for routers off the shelf (just search google for router power backup). But looks like due to the high demand, some products are no more available and some other local manufacturers have paused accepting orders. So the best way is to do it yourself. It’s not that difficult and it’s comparatively cheap.

What you will need:

1. Three 18650 batteries:

This will be the battery we’ll be using. The voltage is 3.7v and you can have it in different capacities. What I got was 3200 mAh ones and with these batteries, I could run a Dialog HBB router for 17+ hours.

2. A BMS (Battery Management System):

Just connecting the 3 batteries in a serial manner and plugging a 12V charger is not the way you should charge them. If done so, the batteries will overcharge and you may face unexpected consequences. A BMS would help you to charge the batteries to the correct voltage, avoid overcharging as well as avoid over-discharging.

The BMSs for 18650 batteries come with different ampere counts, and you’ll mainly see 3 variations 10A, 20A, and 30A. A 10A one is more than enough for a router and I suggest you buy a 10A one.

But be careful, make sure that the BMS has both over-charge and over-discharge protection. I bought a 20A one and during testing, I got to know that it only has over-charge protection but no over-discharge protection.

HX-35-01 is the model number of a popular 10A BMS, and I suggest you buy that. If you don’t find the exact BMS, just look for a “3S 12V 18650 10A BMS” (3S means 3 batteries in serial) that has both the features I mentioned.

Popular 10A BMS: HX-35-01

3. Two “3 Sections 18650 Battery Spacers” or a3 cell 18650 battery holder

You’ll need something to hold the batteries together. If you like soldering the batteries, you can buy two spacers that would fit three batteries.

Soldering the batteries would be a little difficult task. You can try a battery holder instead.

18650 3-cell battery holder

4. DC power sockets

You’ll need to have 1 DC female socket (with nut fixing) to get the 12V in to charge the batteries from a power adapter and 1 DC male plug which you can use to plug into the router

5. 12V Power Adapter (2A or higher)

You will need to buy a 12V power adapter to charge the batteries and power up the device (router). Usually a router would consume 1A or less. Hence, the power adapter that comes with the router should be one which outputs 500mA or 1A. It won’t be enough to charge the batteries and power up the router at the same time. Hence it’s ideal if you can find a 3A power adapter, at least find one with 2A output.

6. Small switch

Optionally, you can use a switch to turn the battery supply ON/OFF. If you are keeping the router on 24/365, you don’t need a switch.


Do the soldering

Now what you have to do is to correctly solder to connect the above components.

Connection Diagram

Follow the above diagram to connect all our components together by soldering where necessary. Though you are using some other BMS, the diagram should be almost similar. If you are soldering the batteries, you may need to scratch a bit in the nodes before soldering. Having a switch in-place as shown above, you can turn on/off the power out when needed.

After soldering

However, before soldering the switch and power sockets, think where you are going to pack these in. For me, an empty Pelwatte butter container did the job.

Before connecting to a router

Before connecting this to a router, you may first plug the 12V power adapter into this and keep it for few hours for charging. Time to fully charge will depend on your power supply as well as the capacity of the batteries. After few hours, you may disconnect the power adapter and check the voltage of the battery output using a multimeter. If it’s fully charged, the voltage should be 12V (if the power out cable is too long, this might be little less than 12V).

If it’s not 12V keep it for some more time and check again. But if the voltage remains the same as the earlier value, use a multimeter and check the voltages of each cell. Specially if you have manually soldered the batteries, there’s a chance that the wires get detached. Verify all the wires are well fitted and do the charging again.

You are done! You can keep your router connected to this 24/7. No more internet interruptions due to power outages.


The prices and product availabilities are varying very frequently. However, I’ll list the cost of the items when I bought them on 17 March. I bought everything online.

  • 20A BMS – Rs. 415
  • 3 Sections 18650 Battery Spacer x 2 Pcs – Rs. 110 (Rs. 55 each)
  • Battery 3200mah 3.7V 18650 Rechargeable Li-Ion x 3Pcs – Rs. 1,725 (Rs. 575 each)
  • Power Supply Adapter 3 PIN AC/DC 12V 2A – Rs. 640
  • DC Female Socket-022 5.5×2.1mm – Rs. 25
  • DC Male Plug 5.5mm x 2.5mm – Rs. 30
  • Small Boat Rocker Switch – Rs. 45

Total cost is Rs. 2990/=

Things to note

The max voltage we can get through this setup is 12V and while discharging the voltage decreases. For a router, this won’t be a big issue. In most cases it would simply stop working after the voltage drops below a certain value. If your BMS supports over-discharge protection, the BMS would cut-off the battery output at around 10.25V. In my battery pack, I discharged it from 12V to 10.5V running a Dialog HBB router (ZLT S10) for 17 hours.

Other solutions

Similar mini power backups

You can buy similar mini power backups from different vendors. Bravo solutions have a similar product range (no endorsement or affilation. I’ve just used one of their products). Also you may search for “Router power backup” or “Mini UPS” and find some other vendors as well.

UPS based battery backups

Several people are using a UPS powered by additional batteries and a battery charger so you can power up your laptop and router for couple of hours. You may find more info regarding to this if you do some searching

Power Station

This is a portable device with a buit-in battery and inverter. You may see more details here.

Power Wall

This is a device which can be setup in your house which includes batteries and inverters in-built. You can either charge from the grid power and also from solar panels. You can power the whole house using this. See more details here.

DIY Solar powered power backups / Off-grid solar setups

I would say that this is one of the most trending topics. The definite place you should go is to DIY Off Grid Sri Lanka group

Further readings


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