Dive flagRebuilding Nikon SB-104 Battery Packs

Chuck Tribolet

Notice: This page tells how I have replaced 1600 mAH NiCd cells with 3800 mAH NiMH cells.  It's worked for me, but if you do it, it's entirely at your own risk.  Some potential problems are:
  • The Nikon charger doesn't detect that the cells are fully charged and continues to charge them, ruining the cells, melting down the battery pack or charger, or, worst case, causing a fire.
  • The resulting packs have a very short recycle time.  If you take lots of pictures in a short period of time, the strobe may overheat internally.
The Nikon SN-104 battery packs used in the Nikon SB-104 underwater flash where OK in their day, but:
  • They are getting tired and new replacements are hard to find.
  • Most were made in 1993 and will have been sitting on the shelf since.  There appears to have been one small batch in about 2003.
  • The cells are 1600 mAH sub-C cells, which were pretty much state of the art then, but have been left in the dust by improvements in battery technology.  3800 mAH NiMH cells are available in the same size today.
  • They are expensive: $130 at B&H.
So the answer is to rebuild your existing battery packs.  The page shows how I have done some of mine.

There's an old recipe for rabbit stew where the first step is "catch a rabbit".  Well, first we have to get the new cells.  I ordered Intellect IB3800 cells from http://www.batterystore.com for $38.70 a pack.  Note that Intellect also makes a 4200 mAH cell, but they are slightly larger, I wasn't sure they'd fit, and the old Nikon 1600 mAH cell were adequate anyway.  I chose the Intellect cells because they have a low internal resistance, which yields a slightly faster recycle time.  The battery store will make up the pack for you for $4.00 -- do this, you really don't want to be soldering on to the batteries themselves.  I didn't have them set up the packs for thermal fuse.  I'll attack that problem the next time I order cells.  Note: do not  attempt to solder the thermal fuse on -- it willl get hot enough to blow the fuse. 

Update: 06/15/2012: The Intellect cells are no longer available, but Elite has high-rate sub-C cells in 4000 and 5000 mAH.  I rebuilt four packs in 2011 using the Elite 4000 cells.  I'd probably try the Elite 5000 next time around.   http://www.batterystore.com  has the Elite 4000 and 5000 cells.  Also, I've stopped putting the thermal fuse in, it's just too hard to not blow them with the soldering iron.  I have batterystore.com make up packs of six cells.

And a note for all you SB-104 users: Check them with a flashmeter.  Of five "functional" SB-104s, I found
that three were way off in 1/4 and 1/16 power.  Some were high, some were low.  1/4 and 1/16 can be tuned with variable resistors inside the flash.  I have the factory service manual, and a dead SB-104 I'm willing to dig into.   If it works, I'll post a web page.  No guarantees as to when though, because I still have two good ones.

Update: 06/23/2012.  Phil (I don't his last name) came up wth an improvement on my razor saw.  He clamped a box cutter handle (aka utility knife) to the work bench and used that.  No saw kerf at all (not that a razor saw leaves much of a kerf) and no sawdust.  I think I'd take it a step further and use just a box cutter blade, with one screw through the hole in the blade and another behind it to keep it from moving.  I'd let just 1/8" f the blade protrude past the block of wood.

Phil also pointed out that the top and bottom of the plastic part are secured to the top and bottom of the batteries with double-sided foam tape (aka telephone tape) and it can take a bit of force to separate them.

Cutting the battery pack openThe first problem is to open up the battery pack.  The first time I did it I just used a razor saw (Proedge #01370, 30 teeth per inch, 1.5" deep, 5" long, $2.79 on sale at the local hobby shop) and, while it worked, it was tedious and the results weren't as clean as I'd like.   So I built a fixture to hold the razor saw just the right height off the work bench, and I slide the battery pack back and forth against the saw.  This results in a very thin clean cut.  Note that the c-clamps are clamping on the blade of the saw, not the back bone.  Also note that there are few pieces of paper under the plywood to shim it to just the right height.
Another view of the fixtureYou don't want to use a hacksaw as that would result in a wide saw kerf and the battery pack would be thinner when reassembled.
Construction details of fixtureHere's what the fixture looks like inside.  There's just a groove for the backbone of the saw, and a little extra bit cut out  for where the handle attaches to the blade.
Opened battery packHere's what it looks like when it's opened up.
Battery detailsHere's a closeup of the original battery pack.  Note the connections on the left-hand cells that go down into the middle of the pack.  This is a thermal fuse, it will blow if it gets too hot, or if there's too much current.
Battery pack detailHere's the other side.
Battery pack detailNote the lump inside the black heat-shrink tubing in the lower right.  That's a diode so you can't accidentally discharge the battery back through the charging port.
New battery packHere we have the new batteries as delivered.  Note that there are no holes in the tabs to solder the old connectors onto.
New battery pack with holes punched in the tabsSo we punch a couple of small holes for the wires to the old connectors.

Partially assembled battery packNow we have inserted the new batteries into the bottom of of the pack.
Assembled battery packAnd we put the lid on and label it with what's inside and the date.  A little Scotch Magic Tape to hold it together and we're done.

Note that the first charge will take several hours.  Remember that we have to pack more than twice as many electrons in there, and that takes time.