Hello, this is my first post on this forum so if I have done something wrong please don't kick me out right away. Feel free to shout at me though.
I just got myself an old motorola c121 mobile phone for playing with
OsmocomBB project. I got it for 30PLN (which is about $10) as in "perfect working condition" with original battery and charger. Before potentially bricking it with osmocom firmware I threw in my backup SIM to see what is it like as a phone (it was fun experience to see stopwatch feature being translated into polish literally as "stop watch"). I quickly noticed that phone does not indicate charging the battery in any way (this may be by design, but I doubt it) and battery status indicator always shows full charge (when i was looking at it at least). Otherwise, it was working just fine. Later, when I was playing with flashing software I had some communication issues (which were my own fault btw) so I decided to tear down the phone to see if there are any obvious signs of damage.
What I saw disgusted me at first and after some more probing terrified me a little. There was obviously some failure in power/charging circuitry and someone attempted to repair it by
shorting positive terminal of charging connector to positive terminal of the battery. I have verified that it is indeed a dead short. Now, this is why there is a question mark in the topic of thread. I am not a qualified EE but an unexperienced hobbyist. For me this is clearly not a way to treat a Li-ion battery but I am curious if it's as outrageous and dangerous bodge as I think.
Here are the facts:
- Charger has nominal charging voltage of 6.4V. Measured voltage is about 5.5V
- positive charging terminal is a dead short to positive li-ion battery terminal
- Negative battery terminal is NOT shorted to ground. There is some circuitry in between
- When charger is connected there is charger voltage (~5.3 under load) present at battery terminals at all times
edit: probably not true and I screwed the measurement. It's difficult to get to the terminals with the battery in place. There is 5.3V on the terminals when the battery is not there though- Phone works without battery inside when charger is connected and shows full charge on battery gauge
edit2: battery gauge actually seems to be a software issue. ADC seems to work fineI am curious about EEVblog community opinion on ingenuity of the guy who had done this. In fact the phone after this fix may be quite useful considering I managed to finally run osmocom bb stack on it and it works without battery inside.