Introduction: Mega Power Bank

Picture of Mega Power Bank

Here's a super-sized power bank, able to keep all your gadgets charged many times over. It offers both USB charging and a 12V accessory socket - with a suitable inverter you can even power small mains devices. It also features a digital voltmeter, to allow the state of charge to be judged.

The design here includes a rugged, waterproof case, with a storage compartment for leads and accessories. It's ideal for a camping trip, particularly when paired with a solar panel for recharging.

Step 1: Collect the Components

Picture of Collect the Components

The main components for the build are:

  • An (empty!) ammunition box. The one I used was a .30 (7.62mm) calibre ammo box, measuring 25 x 8 x 18cm approximately. These are readily available from Army Surplus stores or a number of eBay sellers.
  • A 12V sealed lead-acid (SLA) or valve-regulated lead acid (VRLA) battery. This needs to fit in your ammo box with plenty of height to spare. I used one measuring 15cm x 6.5cm x 9.5cm approx, which is a common sized replacement for UPS units. Typically these have a 7Ah or 9Ah capacity rating.
  • Panel-mounting 12V socket, USB charger, and DC voltmeter set. These can be found on Amazon searching for "12V three hole panel". The three sockets are attached to a plastic mounting plate, but can be removed if required. In this design they are attached directly to the front panel and the mounting plate is not needed.
  • A chunky toggle switch - this can be bought from many electronics suppliers, or a car or caravan accessory shop.

You'll also need:

  • Wood for the front panel - this should be a decent (10-12mm) thickness as it's a structural part of the whole design - and a number of other offcuts of thin sheet plywood or similar.
  • A short length of aluminium angle.
  • Wire, solder, and battery terminal connectors (these are often supplied with the panel socket set).
  • Thin foam for battery mounting - the stuff I used was saved packaging from a laptop case.
  • Nuts, bolts, wood screws, and double-sided adhesive tape.

Step 2: Battery Mounting

Picture of Battery Mounting

The SLA battery will sit on the base of the ammo box, held in place on three sides by the walls of the box. I cut some thin foam sheet to size and stuck it with double-sided tape to the walls. The fourth side of the battery is held in place with a piece of aluminium angle, cut to fit the width of the box. Drill a 5mm hole in the centre of the angle, then fix another piece of foam to its other face. Put the battery in position, hold the angle up against it, and mark through its hole onto the base of the box.

Drilling the hole through the base of the box is fairly straightforward if you have a Dremel or similar small drill which will go in the box. If not, you may need to mark the position with a centre punch, then drill through from the other side. On my box the top lid was detachable, which made it easier to handle during assembly.

If all goes well you can attach the aluminium angle to the base with an M4 bolt and Nylok nut. Make sure it's good and tight as it has to restrain the heavy battery.

Step 3: Front Panel Construction

Picture of Front Panel Construction

The front panel is a piece of softwood cut to fit inside the ammo box. The sides of the box are slightly tapered, and the corners are rounded, so I found it easiest to cut out a template from cardboard first and trim it for the best fit, then draw round it on to the wood. I rough-cut it using a power saw then shaped it, first with a surform and finally a power sander.

The final width of the panel is a balance between keeping a comfortable spacing between the sockets, and leaving a good width for the storage compartment. On my box it came out as 175mm, as measured along the centre line.

Next, cut holes for the three 12V sockets and the switch. I used a 30mm hole saw and a 12mm wood bit, respectively. The spacing between each of the hole centres came out at 42mm. I also needed to chisel out a rebate on the reverse of the panel to allow the switch to poke through sufficiently.

When the wood is cut, it can be finished as you fancy. A medium wood dye and a couple of coats of glossy yacht varnish will give it a rather nice 'vintage car dashboard' look.

Step 4: Front Panel Wiring

Picture of Front Panel Wiring

When the woodwork is ready, the power sockets can be mounted on the panel, then wired up. I decided to leave the 12V accessory socket unswitched (connected directly to the battery), and the USB charger and voltmeter connected via the switch. They have a small (40-50mA) power drain when on, so will discharge the battery gradually if not switched off.

When finished, the wiring looked as shown in the photo. I put heat-shrink sleeving on the finished joints to provide mechanical support and avoid exposing any 'live' conductors should any stray bits of metal find their way inside. You can briefly test the wiring by connecting up the battery, before further assembly,

Step 5: Battery Top Mounting

Picture of Battery Top Mounting

The heavy battery needs to be held securely in place to prevent vertical movement. This is done with a wooden 'channel' which sits on the top of the battery and is held down by the front panel. The channel is made with a small piece of 6mm ply, cut to the width of the battery, and two wooden offcuts (25 x 12 x 150mm approx) for the sides. These sides need to be tall enough to allow clearance for the front panel sockets and their wiring.

The sides have a step cut in one end to leave a gap for the battery terminals. They are glued to the ply, and held in place with a couple of panel pins. (I made sure the heads of the pins were punched below the surface so they didn't scratch into the top of the battery).

When this is done, the channel piece can be placed on top of the battery, and the front panel is then put in place above it.

Step 6: Final Assembly Steps

Picture of Final Assembly Steps

The front panel is held in place with four screws, two on each side. You'll need to drill holes in the ammo box at the right position to hold the front panel in place - I found this easiest to do by measuring the distance from the top edge to the face of the panel (see photo), then adding on half the thickness of the wood. Position the mounting holes so that the screws avoid the the DC sockets when fully inserted.

Finally, you need to cut a piece of thin ply to form the side of the storage compartment. It can be held on to the right-hand edge of the front panel with a couple of veneer pins. When this is done, the panel can be pushed into place and the mounting screws put in.

Step 7: In Use

Picture of In Use

Lead-acid batteries are fairly forgiving (compared to other battery types) of electrical abuse, but their performance and lifetime will be improved if treated properly. I'm using a proper microprocessor-controlled charger to recharge the power bank - this has a multi-stage charging cycle, finishing with a 'float' stage which holds the battery fully-charged indefinitely without damaging it,

The voltmeter can be used to judge the state of charge of the battery. During discharge the voltage will drop from 12.5V or so to under 11V - it's not recommended to discharge below about 10.5V as a deep discharge can permanently damage the cells.

You can use a solar panel to recharge the battery, but note this will usually be a 'top-up' rather than a full charge - a 5W panel will charge at 0.3 amps or so in full sunshine, which will need 25 to 30 hours to deliver a full charge. Don't leave a solar panel permanently connected if the voltage is capable of exceeding 13.8V or so.


Ytprivilege (author)2017-12-12

Add a small fan for outside usage. Will help charge the battery with or without solar.

jerry.ericsson2 (author)2017-08-08

I do like the idea, but to save weight, I think when I build mine I will go with recovered 18650's from old laptop battery's. I have about twenty five of them now saved up for such a project, and have several small power bricks that I built with plugs on them so they can be plugged into various devices. One has a step down converter so I can use it for most of my 5 volt projects, another with a step up for 12 volt and up projects, and the big boy I have is set at 32 volts to use with my 50 watt and 100 watt led lights.

lapsmith (author)2017-01-03

To be safe, I would make sure the ammo box is vented. I don't think SLA batteries are supposed to give off (much?) hydrogen when charged, but I wouldn't take a chance. One spark inside the sealed box, and it could go boom. Someone here at work died when a liquid electrolyte lead acid battery in a sealed box blew up as he was bending over it.

TheSpodShed (author)lapsmith2017-01-04

The battery datasheet does indeed say "on no account charge the battery in a sealed container", although in this design you can't connect anything (for charging or otherwise) when the lid is shut. On mine the wooden side panel is a loose enough fit that the battery compartment is nowhere near gas-tight, when the lid is open. You could drill a few small holes in it to make sure, I suppose.

Ooo! You could install a tube and collect the H2 gas in a balloon for fuel! KIDDING! Oh please nobody try that!

This is very cool and handy... I may have to try building a backpack version if I can find a more suitable (lighter) case of similar dimensions. Ideas?

RobPaige (author)oolon colluphid2017-08-08

Plastic ammo cans are lighter, but the real killer in terms of weight is going to be the battery.

kz1 (author)oolon colluphid2017-08-07

Harbor Freight sells a plastic ammo box that might work??

bscgvrvr (author)2017-08-07

How are you going to regular the voltage from 12.5 to 5 volts and amp from 7.5 to 500-900mA

leseagle (author)2017-08-07

To secure the battery you only need to use a little Hot Glue...

VirginiaJ5 (author)2017-08-07

Looks like a great power source! It also looks very Steampunk! Great way of killing two birds with one stone!

leseagle made it! (author)2017-08-07

I have worked on perfecting this design with probably 10 prototypes for the last 5 years. I call it my iGet, iHold, and iUse Personal Solar System. Check out my design it includes everything you have here but all are controlled by a solar charger. I also have a direct input for charging from the wall plug. In addition it has a 48 LED flat light that will light up a room with 180° full spread warm or cool controlled by a mini SPST switch. It has a small barrel connector so you can directly plug in power for small scaled 12V lighting and devices. It also includes a lighted switch so you know it is one and off. The case is $4 at any Menard's and is a look a like but larger in width shell case all in plastic with a rubber bead top with nice ego handle that folds down flat so you can stack them.

leseagle made it! (author)2017-08-07

Looks good but limited to charging in the wall... just add a solar charger and you can charge it anywhere. Q... when the 3 electronic devices come with a plastic pre-drilled and mountable plastic face... why didn't you just cut a slot and drop it onto your base and screw it in... hum seems like you went to too much work for that part... also looks neater with the plastic. I have worked on perfecting this design with probably 10 prototypes for the last 5 years. I call it my iGet, iHold, and iUse Personal Solar System. Check out my design it includes everything you have here but all are controlled by a solar charger. I also have a direct input for charging from the wall plug. In addition it has a 48 LED flat light that will light up a room with 180° full spread warm or cool controlled by a mini SPST switch. It has a small barrel connector so you can directly plug in power for small scaled 12V lighting and devices. It also includes a lighted switch so you know it is one and off. The case is $4 at any Menard's and is a look a like but larger in width shell case all in plastic with a rubber bead top with nice ego handle that folds down flat so you can stack them.

Sandre01 (author)2017-08-07

Very Nice

barntt1 (author)2017-01-22

Safety FIRST.. You forgot the FUSE! Great way to burn down a house! Install the safety equipment (THE FUSE)

JohnnyVerhoeven (author)2017-01-15

Good idea. I would use a small li-ion battery designed for motorcycles. They have all electronics on board to charge and protect it. I have one in my motorcycle. It was a simple swap with the lead battery. It works like a charm.

jjarrett1999 (author)2017-01-02

I think this is great and I love all the comments! This is so bare-bones easy, anyone can do it without needing to know anything about electricity. We camp long weekends and have a handful of little phone chargers that get lost, cords get lost, etc. A single bank for everyone would be great. I bet you could re-charge this off the car battery while going to buy ice and such as well. Working with Lithium batteries at work, I'd agree you absolutely cannot replace the UPS battery with any Lithium battery without charge-protecting circuits and fuses - laptops, phones, hover boards all burning up...very important to get the charge just right and prevent both over-discharge and over-charge. Considering my 12,000 mAh charger with solar is tiny compared to this battery, Lithium is a big step forward BUT requires much more research and money. THIS 'ible is awesome as either 1) a lower cost, safer alternative, or 2) a great low gradient to get in there and actually just do something.

As someone who used to replace UPS batteries, the Batteries-Plus UPS batteries only last a year maybe two whereas the OEM APC batteries last 2-3 years in an APC UPS. This is a place where you get what you pay for. Considering the chance of over-discharge cutting the life of the battery without some more circuits added in, I'd probably still go with the cheaper batteries myself ;-)

smpcorp (author)2017-01-01

One of, if not the most practical projects I've seen in Instructables. Nice job!

PaulA3 (author)2017-01-01

The only area I can see could use some improvement is the bolts through the ammo case could be waterproofed. It looks like a waterproof/water resistant ammo case. The bottom to the top is anyhow. If the case sits in a puddle I can see water leaching in through the bottom hole. I may build one of these for my boat to charge and protect my devices from water.

Rustic Woodcrafter (author)2017-01-01

Literally made one 40 years ago to provide backup power for video camera and sidepack. Used motorcycle lead acid battery, charger and 12V socket. HEAVY. This build is so much nicer and the solar recharge adds a whole new dimension. Thanks for the memory!

badmammajamma99 (author)2016-12-24

this is rocking! fantastic job on the construction of this tin can of wonder! im not an electrician, i know nothing about batteries other than dont lick the 9 volts, and im totally confused about the terms, types, and this and thats as far as the tequnical side goes. think i should read up before trying this and have a buddy who knows what he is doing help?? or just boy scout the whole process and follow the instructable. again, i think this is a gorgeous project... very well done.

RaymondM58 made it! (author)2016-10-11

Made this for camping, and will not get to try it out till next spring/ summer. Almost destroyed the 12v plug trying to solder the wires on it. Ended up taking the plastic off the connectors and slipping heat shrink over them. Now all i need to do is add a way to charge it. Some advice on this would be much appreciated.

TheSpodShed (author)RaymondM582016-10-15

Glad to be of service, and thanks for the pictures!

Charging works through the 12V socket - it's just a direct connection to the battery so wiring up a suitable charger to an accessory plug does the trick. See step 7 for a pic of what I'm using. For keeping it topped up you can use a 12V solar panel - these are often sold with a plug attached.

Thanks - Ian

ZachB18 made it! (author)2016-09-21

Made this for camping and LARPing with Dystopia Rising. works great for charging devices. I included a trickle charger for a motorcycle with a 12v plug for chargin in the field and added a fuse between the battery and the plugs to protect pulged in devices.

TheSpodShed (author)ZachB182016-10-15

Well done sir! Thanks for posting the pic - enjoy your LARPing.


JamesS511 made it! (author)2016-08-26

This is pretty awesome. Great idea! I picked up a solar panel for charging and made car and 120V adapters!

rcolon179 (author)JamesS5112016-09-18

This is a great set up for camping or even fishing! Very simple. Thanks for the pics

TheSpodShed (author)JamesS5112016-08-29

That's brilliant - thanks for posting your photos, I'm genuinely flattered. Hope you find it useful,


rsmaudsley (author)2016-09-09

I made a similar device but used three 6VDC batteries to make an 18 VDC power source. I needed it for a water mister\fan for our chickens when we had 105+ degree heat. The original battery would only last an hour or so. This battery pack ran the fan for two days.

Any ways, for the ammo can I used this product from Harbor Freight Tools and it worked perfectly. And for $8 it's much cheaper than trying to buy the metal ammo cans from a surplus store.

rncbme (author)2016-08-29

Nice job. I believe I will include a fuse of some type in mine. I know just about everything you would plug into it would have a fuse but better safe than sorry ;)

Instructeronimo (author)2016-08-18

Very nice Insctrutable.

However, as an Electrochemist I would like to give some advice:

You should really consider using another battery Type than Lead-Acid. Especially these SLA or VRLA are intended to be used in float applications, meaning in an UPS at full charge all of the time. once discharged below 50% DoD (Depth of Discharge 3.5Ah for the 7Ah Battery) these types will never reach full capacity again due to grid corrosion. Instead, using e.g. 2 18650 cells rated at 2900mAh, you would have much better lifetime at much reduced weight. I would suggest using some kine of LiPo package rated at high capacity instead of Lead-Acid, resulting in much higher Energy Density and increased cycle life.

Sure, lithium batteries are way lighter than lead-acid.

Why I didn't use one: single Li-Ion cells like 18650's are 3.7V, so I'd need 3 in series for nearly-12V, and a 3x2 or 3x3 array for a comparable overall capacity. To charge
these safely & reliably you need monitoring & balancing of the
individual cells; if you get it wrong your expensive batteries die, or catch fire. To be honest it's more complicated than I'm prepared to write up as an Instructable.

For reference, the data sheet for the battery I ended up using is here:

At 50% DOD they suggest 400 or so cycles, or 1200 cycles at 30%. So perfectly comparable to other battery types.



Ondra1342 (author)TheSpodShed2016-08-26

TheSpodShed Its true. Lead-acid battery is safety...I saw a burning phone and it is like hell (because the Li-ion accumulator caught fire - improper use)

Totally right. Plus, it's not Ah that counts, but Wh. That is of course 3 times higher for a 12V SLA Stack than for a single LiPo. I personally am not fond of Li chemistry either. Especially balancing, as you mentioned. Very high risk of Fire! Too bad that reliable battery Technology is still in development. But we're working hard in it...
As said, great instructable!

badrobot made it! (author)2016-08-21

Thanks for the great project! I ordered the parts from Amazon but I don't have an ammo can so I found this little plastic tool box at Lowe's for $4. I used Velcro to hold the battery down and a different power switch but the 12v outlets are the same. The whole thing works great. Just in time for my next camping trip.

ffor fo

TheSpodShed (author)badrobot2016-08-23

Great stuff! I particularly like the illuminated power switch, it goes well with everything else.

Thanks for sharing

AlanS14 (author)2016-08-21

There are more than one lithium technology available for use. Lithium Iron Phosphate would be the better choice for this project, a 4S cell configuration gets you close to a 12V lead battery in terms of fully charged voltages etc, and is safer than the LiPo technology that keeps getting mentioned. It is far lighter than Lead and has a greater energy density (not as high as LiPo though), cells are available with 10C discharge (10 times the charge rate) - look at headway 10A, 12A or 15A cells for example, you can get far more of the energy out that you put in than lead can, and is safe. There are times for lead batteries, but for this kind of project the advantages of LiFePO4 are pretty good.

Razanur (author)2016-08-18

Hi! Cool Idea - I really like the housing as well! I did something similar with an old car battery. From experience, I would really recommend using a good 12V socket like this and a nice USB module (e.g. using the KIS3R33S, like this:, not the nasty china ones. The 12V socket can easily handle 20A (240W) and the USB charger handles up to 3A (so it will not even get warm for providing your phone with 2-2.5A).

Razanur (author)Razanur2016-08-18

(I would also fuse the 12V socket and wire it directly to the battery, not use the switch on it (most switches will die if you switch 20+A with it))

Obsidian Man (author)2016-08-15

I can't find a 12v three hole panel with a socket, do you have a link for the one you bought?

DavidA207 (author)Obsidian Man2016-08-18

They have them on AMAZON...

TheSpodShed (author)Obsidian Man2016-08-17

The one I bought was

Searching just for "12V DC voltmeter" turns up lots of other options, though.

Obsidian Man (author)TheSpodShed2016-08-17

Also im kinda confused about how to charge it.

brew1958 (author)Obsidian Man2016-08-16

Amazon has them for around $11.00 with free shipping. You can get them cheaper if you wait on the shipping time.

LoganW29 (author)Obsidian Man2016-08-16

HarryB80 (author)Obsidian Man2016-08-16

Thay are on ebay too

Yang Xiao Long (author)2016-08-17

Hmm, the lead acid battery is a tad impractical here. I like the concept, but the battery is huge and theres no recharge that I see. This definitely has potential tho...

John-woodwork (author)2016-08-16

How long would battery last?

It depends on what you connect to it. A '7 Amp hour' capacity should supply 1 Amp for 7 hours (or 7 Amps for 1 hour, etc.) In practice you will get less in total the higher the current.

For USB charging a smartphone at (typically) 1A at 5V the battery drain is roughly 0.5A so you should get 12-15 hours charging time.

brew1958 (author)2016-08-16

I've made one of these in a larger scale using a solar charger and 50 watt panel, a type 31 battery and battery box. It is the same thing with much more capacity, but less portability. I can plug a 400 watt inverter into the 12 volt power socket and charge my laptop or run any number of small radios/cd/dvd players etc.... I put a 12 volt fan in the tent and its all good! I use it mainly of an evening or night time when lighting (12 volt solar strips) or music etc... is needed. The one shown here is just smaller but is perfectly designed. Scale it up as big as you want. Great job!

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