Monthly Archives: March 2015

Fixing Battery Corrosion in a Mini Maglight

About twenty years ago or so, I bought a Mini Maglight to supplement one I had bought about twenty-seven years ago. Both of these use the itty bitty incandescent bulbs, neither one being anywhere near new enough for the fancy modern white LEDs. They work, anyway. Or, they did – until the batteries in the newer one leaked.

Normally, this wouldn’t be a big deal. You replace the batteries and get on with your life.  In this case, though, there was a complication. The leaking battery was completely stuck inside the flashlight barrel. I tried banging the open end against the back of legal pad, and I tried that a lot. No good.  Evidently it was time to take it apart and push out the dead cell.

There are at least two versions of the incandescent Mini Maglight running around, and my two were of different generations. I had taken the old one apart before, but the new one was a bit befuddling. First, field strip the easy parts – take out the bulb and then just pull on the “do not remove” outside bulb holder until it pops off.

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This leaves you with the inside bulb holder, the barrel of the flashlight, and one immovable battery. It’s time to move the immovable. I didn’t have a pin punch the right size, so I grabbed a cheap, junky Torx screwdriver that would fit in the access holes at the very back of the inside bulb holder and whacked it with a hammer.

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This resulted in squat. I was deforming and slowly hammering my way into the battery instead of pushing it out. Judo is too subtle, I’m switching to Kyokushin: hit it harder.  About ten good whacks with a small hammer and I started to actually move the battery.  A bunch more and it finally came out.  Finally, switch to a larger drift (in this case a, uh, Uniball Vision ballpoint pen…) and gently tap on it until the inside bulb holder falls out of the threaded end.

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Inspection of the flashlight barrel revealed the reason the battery wouldn’t come out – when the cell leaked, it dumped potassium hydroxide into the bore.  This reacted with the aluminum barrel forming hydrogen gas (always a crowd pleaser) and potassium aluminum tetrahydroxide – aka “crud”.  Oh, and it also formed a corrosion pit in the aluminum – luckily not all the way through the metal.

Cleaning out the corrosion is done with a 20ga shotgun bore brush threaded into a cleaning rod and the tool spun with a drill.  Wear a dust mask and eye protection.  Bear in mind that the friction will heat up the aluminum, so pay attention and stop to let it cool at intervals.

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Assembly is the reverse of dismantling.

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