cmoy dead battery and dc offset?

[tola555]

I use 4 batteries in series, each 9v (total 36v = +-18 for opa2134). It worked nice and one day I checked if I have to replace batteries. They were ok, total 28v or something. I measured DC offset and it was ok too (2.3mV and -2.0mV). Then I measured batteries one by one and two of them died !! now they are 1.5...2 V.

When turning amp on dc offset was ok but started do rise to 150mV in 20 seconds

Its dangerous for my phones

Now I replaced batteries and its stable now.