Testing CMOS Batteries CR2032

E

Executioner

Gawd
Joined
Apr 22, 2015
Messages
758
This is puzzling to me. I bought 2 used Dell Inspiron 17" 7377 laptops cheap because when powered on, the Dell logo would briefly be displayed and then the laptop would shot off.

After I disassemble the laptop, one of the checks I do is the CMOS battery using a Fluke DMM. The CMOS battery shows 2.9 volts. So I continue to trouble shoot not finding anything obvious, so I decided to take the CMOS battery out and short the contacts to remove any residual voltage. Since I had the battery out, I used this battery tester https://www.ztsinc.com/mbt1.html and the CMOS battery is dead according to the tester. Not even 1 bar on the tester. So why would the CMOS battery indicate voltage on the Fluke DMM?

Anyway, I replaced them and the laptops now work fine. I know my Fluke meter works fine, because I checked it with another Fluke meter with the same results. Is this because there is still some voltage in the battery, and if I left it on the DMM, would the voltage would gradually drop?
 
battery voltage is not a complete measurement of its 'health'. You want to know its voltage under the intended load. For the tester i cant find any info on what kind of load it uses for coin cells so i cant comment on that.

*Think Car battery that shows correct voltage but cannot start car*.

It is also possible that the battery was good enough for cmos but maybe had oxide or contaminants in between the contacts and the battery so why it was causing an issue. Did you measure battery voltage on the can of the battery or on the contacts? (do this method to see what voltage is at the motherboard and can help diagnose insufficient contact issues).

Also clearing the cmos may have wiped out an error or configuration issue allowing it to boot up as well.
 
I measured it first on the contacts while still installed on the motherboard. I then pulled it and it still indicated the same voltage. When I put it back in, the laptop still would not boot.
 
Ive had dells do some weird things with low cmos battery voltage too. Other brands seem fine even if they reset the time every unplug, but dells for whatever reason are more picky it seems.
 
mnewxcv said:
Ive had dells do some weird things with low cmos battery voltage too. Other brands seem fine even if they reset the time every unplug, but dells for whatever reason are more picky it seems.
Click to expand...
yup, was dealing with one last week that freaks right out due to that. powers up, shows dell logo, goes blanks, reboots several times, goes blank, eventually throws up date/time error. then you can ignore it and continue.
 
You must log in or register to reply here.
Back
Top