Giving new life to an old nvram IC

[festy]

I had an old DS1245Y with a flat internal battery, and thought I had nothing to lose by trying to fix it. How hard could it be?




Step 1 - remove the ABS outer case. It comes off pretty easy with a sharp knife. just give one of the ends a little squeeze with pliers to get an initial crack in the glue and you're away. It's worth holding the nvram in a sacrificial ic socket to save snapping the pins off if you get too rough with it.
The arrow pointing to the 1 indicates which end is pin 1.

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Next, step 2 - carefully mill the top away until you hit metal. Don't panic, it's only the battery
Of course, milling the surface down removes the arrow indicating pin 1, but that's ok because there's a 1 stamped into one of the ends as well.

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Step 3 - carefully remove enough plastic at one side of the battery so you can stick a blade down to prise the battery out.
it's spot welded in, so hold the bottom contact down with a little screwdriver while you remove the battery or you could rip the terminal out of the casing.
Don't go too deep with the plastic removal, or you'll cut through the pin contacts (I got a bit carried away with the grinder, and had to re-solder a pin to it's lead)

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and lastly step 4 - solder a lithium battery holder onto the two exposed terminals. I used a CR2032 but you could use a smaller battery (or remote mounted battery) if clearance is an issue. The CR2032 has a shelf life of 10 years, and will die of old age before the nvram could drain it - I would have used a smaller battery but that's what I had on hand. The original BR1225 is only 48MAh, so this one is way overkill.

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So despite what Dallas says, you CAN replace the batteries in these!
So don't chuck out your old ones when they stop working, just replace the battery

[Jayme]

great stuff ill be trying this one out in years to come

[antus]

Love your work festy

[VL400]

True DIY Out of interest how old was the original? There is a date code on them, under the "NONVOLATILE" text the first string of numbers is year and maybe week of manufacture eg 1122C on my current batch is 2011 and maybe 22nd week.

[festy]

This one had a mid 2003 build date.
It's interesting that Dallas's datasheet states an expected cumulative data retention of a minimum of 10 years, yet the datasheet for the BR1225 lithium battery inside it lists a lifespan of "up to 10 years".
The NVRAM's initial battery disconnect mode doesn't stop the battery ageing, and the NVRAM build date isn't the battery's build date - the battery could easily be 6-12 months old at the time it's encapsulated so I'm not surprised this one lasted <8 years, I think 10 is pretty optimistic.

Edit - actually the CR series have a 10 year shelf life, the BR series is only 7!

[VL400]

Yeah now knowing what battery it is the 10 years is pretty unlikely, and the way they are used in a vehicle will take more of a toll on the battery than equipment thats on more than off.

[festy]

That new battery would keep the nvram going for over 40 years if the electrolyte lasted that long