NiCd battery replacement in vintage computers

[Lyndon Nerenberg]

> On Feb 6, 2016, at 5:31 PM, Maciej W. Rozycki <macro at linux-mips.org> wrote:
> 
>> Voltage?  Recharging circuits?  Current sinking capacity.  It's not 
>> always a 1:1 mapping.
> 
> Sure, but does it really matter in a typical battery-backed-up RAM or RTC 
> application seen in computers?  I swapped the dead original NiCd pack for 
> a compatible NiMH one in my DECstation 2100 some half a year ago and the 
> machine seems rather happy about the replacement.

It all depends on your definition of 'typical'.  In most cases, a NiMH coin cell will happily replace a NiCd one.  But it's not always a 1:1 mapping.  It never is if 'recharge' is uttered in the sentence.

You need to spend a minute looking at the circuit before declaring MH <==> NH.  It's no different than when you make any other part substitution.  But when you're mucking around with something that *feeds* power into a circuit, it's worth paying a bit of attention, lest surprises come along.