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Newbie Question - Building a quick battery tester


New Member
I just replaced the power loss, memory protect, rechargeable battery in my very old phone system with a slightly different one because I couldn't find a direct replacement. I'm pretty sure that the new battery will work. the old one was a 2.4V 100mah Ni-Cad and the new one is 2.4v 500mha LI

After giving the battery 24 hours to charge I want to test that it successfully was charged by the phone system. Obviously I don’t want to test it in place because if it didn't successfully charge I don’t want to loose all of my programming. Using a volt meter and a resistor can I build a quick battery tester to test that the battery charged?
What value resistor would I use as my load?
Would I be measuring the current that battery is delivering or the voltage?


Nigel Goodwin

Super Moderator
Most Helpful Member
Don't do it!!!!

Li-Ion is completely different, and 4.2V not 2.4V - unless you mean something different by LI?.

Replace the battery either by NiCd (such batteries are freely available for exactly this reason), or NiMh (which is 'near enough' for the crude charging employed).

Wrongly charging Li-Ion is HIGHLY DANGEROUS, and can easily cause the battery to burst in to flames.

Nigel Goodwin

Super Moderator
Most Helpful Member
You should be OK then, just stick it in and let it charge - as I said, such phones only use crude charging systems (like one resistor!), so work equally well with NiCd or NiMh.

There's no real way to make a sensible battery test meter for NiCd/NiMh, the only way is to monitor it's voltage while it discharges at a known rate.

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