Newbie Question - Building a quick battery tester

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?

Thanks

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.

Do you have pictures/links to your old and new battery?

Mike.

This is the original battery (I didnt want to use this one from Amazon because it is not OEM and these Chinese batteries dont last very long. I also need it next day becasue they are turning building power off today)

and what I replaced it with it is NI-MH, not lithium - shouldn't post after a few drinks

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.

Thanks. Guess I'll see what happens when the power goes out today!