I have a wireless phone and recently i had to replace it's lithium battery.
The previous battery was totally dead and would work for like 30 minutes or 1 hour before it showed the "low battery" indicator and a single 3 min phone call would totally kill it and shut down the device.
I left the new battery charge for a good 20hs and after about 15 hours of light use (mostly standby while not being in the base) it shows a low battery icon, the manual says it's supposed to last for 7 days in standby with a 300mha battery and the new one i got is 750mha, even if the battery is really crappy i guess it should last at least the same.
Any chance this is related to how that phone knows how much battery is left? I read that there is no reliable way to know the charge left on a lithium battery just by measuring it's voltage so maybe the phone just tries to "remember" the previous cycle lowest voltage to try to estimate how much is left? if this is the case then the new battery would need to run a full cycle before the phone can reliably tell the charge? (kind of like laptops).
How does it work?