notbob wrote:

On 2010-08-24, john hamilton wrote:
I'm replacing a small button battery (CR 2032) with two AAA batteries,
I'm intending to leave the old discharged button battery in its place and
solder the leads from the AAA batteries directly on to the button
battery.

As I understand it, batteries not only lose their charge, but in dying
they build up a very high internal resistance, also, so you don't want
to leave a dead battery in the circuit.

Did you mean to say "a very low internal resistance"? If so, the
conclusion (that you don't want to leave it in circuit) would make
sense, but as written it is illogical, unless you think he wanted
to wire the new battery in series with the old one.

My understanding is that he simply wants to re-use the old battery
as a connector by means of which the new batterty will power whatever
circuit the button battery did. This implies wiring it in parallel.
Thus to prevent unwanted excessive draining of the new battery by
the old one, the higher its resistance, the better. Of course it
may not have the same resistance in both directions.

It ought to perfectly OK to solder wires to AA-type batteries (I've
done it myself to rechargeables when I wanted to replace a welded
multi-pack for which a replacement was unobtainable). I'd be less
happy to try it with button cells.

On balance, I would advise against his cunning plan. He'd be better
throwing the button battery away and -if he really wants to replace it
with AAAs- soldering some wires directly to the button battery holder.