An eBay purchase of an old Fluke 731B soon showed that although it worked reasonably well (quick fire up only) and was able to charge its internal NiCad batteries, they did not hold charge for more than an hour or so. Opening it up revealed a bit of 'battery cancer' which had also wicked down the cable to the main board. An EEV blog postee ( I can't find the post now!) had had good results with routine rechargeable batteries. I had a few (well quite a few) eneloops (700mAHr) lying around. I like the retention of charge feature of eneloops.
I used the technique in the Mr Carlson's Lab Youtube (making a new battery for a Tek 200 series mini-scope) to solder the batteries together. sandpaper, flux, solder quickly and have an IPA soaked rag handy to cool off rapidly after.
New connectors and a good clean of the PCB.
A quick current measurement showed a charging current of 18mA (~0.025C) on mains and a battery draw of 8mA when switched on but not connected to the mains.
Hopefully they will last a while.
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