Canon NB-5L Battery Teardown, Cheater, and Voltages

The motivation for gutting that Dell laptop battery was to find out if the cells could become a higher-capacity external battery for the Canon SX230HS camera. Those discharge curves suggest they can’t, but I also want to know what voltage levels correspond to the various battery status icons, which means I must feed an adjustable power supply into the camera… so I need a fake NB-5L battery with a cheater cord.

The first step: crack the case of the worst of the eBay junkers. I squeezed it in the bench vise to no avail, then worked a small chisel / scraper (*) into the joint. The lid was firmly bonded to the case, but it eventually came free:

NB-5L Battery - opened
NB-5L Battery – opened

The protective PCB sits at one end of the cell, with a strip of black foam insulating the components from the nickel strips:

NB-5L - protective PCB
NB-5L – protective PCB

It turns out that the cell’s metal shell is the positive contact, which I didn’t expect.

The component side of the PCB has a 10 kΩ resistor connected between the center and negative contacts. That should be a thermistor, but it’s a cheap eBay knockoff and I suppose I should be delighted that there’s not a gaping hole where that contact should be. The PCB fits against the small notch in the case and is held in place by small features on the top and bottom. The negative contact is on the far left:

NB-5L - PCB interior view
NB-5L – PCB interior view

Canon sells an AC adapter for the camera that includes an empty battery with a coaxial jack that aligns with a hole in the battery compartment cover. I soldered a pair of wires to the PCB, drilled a hole in the appropriate spot, added some closed-cell foam and hot-melt glue to anchor the PCB, and made a cheater adapter. For the record, the orange wire is positive:

NB-5L - gutted case with pigtail
NB-5L – gutted case with pigtail

It turns out that the camera battery cover must be closed and latched before the camera will turn on, but the sliding latch mechanism occludes the hole. This cannot be an inadvertent design feature, but I managed to snake the wire out anyway.

Connecting that up to a bench supply (with a meter having 0.1 V resolution) produces the following results:

Voltage Result
3.8 Full charge
3.7 2/3 charge
3.6 Blinking orange
3.5 “Charge the battery”

The camera draws about 500 mA in picture-taking mode, about 300 mA in display mode, and peaks at around 1 A while zooming.

The Genuine Canon NB-5L is good for 800 mA·h to 3.6 V, as are the two best pairs of the Dell cells. The latter remain over 3.7 V for 500 mA·h, which suggests one pair would run for about an hour before starting to blink. Maybe that’s Good Enough, but … a new prismatic battery is looking better all the time.

(*) Made by my father, many years ago, with a simple wood handle that eventually disintegrated. I squished some epoxy putty around the haft and covered it with heatshrink tubing, but (now that I have a 3D printer) I really should print up a spiffy replacement. I’ve been using it to pry objects off the printer’s build platform, so that’d be only fitting…

14 thoughts on “Canon NB-5L Battery Teardown, Cheater, and Voltages

  1. Red and Black Sharpies, or Red and Black heat shrink are good ways to correct non-conventional color coding… a bit cheaper than a large stock of each color of wire in all the gauges.
    – Steve

    1. Yes: Sharpies FTW and I loves me my heatshrink tubing!

      I stripped those wires from of a hunk of ribbon cable, only to encounter the sliding battery compartment latch: that kludge has definitely outlived its usefulness.

      A cheap external power pack should arrive shortly from halfway around the planet, complete with a fake NB-5L battery and a suitable connector. Even though it’ll surely require a rebuild, starting the process with bigger pieces may end well.

    2. Yeah, I decided I wanted all the colors in just one gauge, and one type (stranded), and it was surprisingly expensive. But I’m glad I did it. So glad, in fact, that I made a celebratory graphic:

      1. Happy dance!

        Obviously, though, if you had enough wall space for that rack, you didn’t have enough stuff

      2. DOOD!!! I like the way U Think!
        And, most certainly you did not have enough Stuff.
        I get my wire free :-)
        1 perk of being an electrician

  2. Purchased a month ago Canon PowerShot SX130 IS for 127€. A heavy duty construction (308g), nice pictures, but got to be the “thirstiest” digital compact camera on the market.

    1. Even though I’d guesstimated the current draw at half an amp, I was still surprised that it’s that high. Those crap eBay batteries definitely aren’t up to the task, but paying a significant fraction of the camera’s price for one OEM battery seems, well, excessive.

      An external power pack won’t work for anything other than long-duration tripod & microscope sequences. A larger camera wrapped around a larger battery won’t fit in my pocket. We consumers impose such irrational requirements… [grin]

  3. I came across your blog entry while researching the feasibility of an external battery pack for my SX230HS. I want to take some long duration time lapse photos and the NB-5L’s just don’t have the stamina. My approach will probably be to use a 6V or 4V sealed lead acid battery and a power resistor in series with a 3.7V zener diode voltage divider circuit to provide the power. I’ll then connect this to the camera using the AC adapter dummy battery and a barrel power connector.

    1. a power resistor in series with a 3.7V zener diode voltage divider circuit

      That won’t work well, because the camera draws 500 mA at idle and about an amp while zooming. The Zener must conduct more than the total current in order to provide proper regulation over the full range, but you really don’t want to pull 1 A from the battery at all times!

      Given that the camera was designed to run from a single lithium cell, you may as well feed it exactly what it likes, rather than wrap additional complexity around the wrong chemistry. I have one of those cells on the bench, waiting for a Round Tuit to magically appear.

      I admit to feeding 9 V into a radio intended for 7.2 V from two series cells, so you might be able to get away with a direct connection to a 4 V lead-acid battery. However, the fully charged voltage would be nearly 5 V and that seems way too hot for the camera.

      For your application, a larger lithium cell or a battery made of paralleled cells would make more sense. Those batteries may give you some ideas; I’d get one of their chargers to go along with the pack, plus a polyswitch to limit the current and a protective PCB to keep from detonating the cell.

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