I have 4 x 230Ah lead acid batteries (closed, but not gel or AGM). Two in series, both pairs in parallel for a 24V system. The batteries are at least 5 years old, exact age unknown.
A couple of weeks ago I discovered that there are voltage differences in each pair, for example the lower battery had 11,9V while the upper battery had over 13V.
Then I bought the Victron Balancer and installed it. In general it works fine: When the bank is notable discharged (say by 50Ah) and then charged with my Victron Centaur 24/70 the voltages are pretty similar during the process.
But a the end of the bulk phase, when there is only about 4A charging current left, something weird happens: The upper battery gets more and more voltage up to 15,1V while the lower battery gets less voltage of around 13,6V.
After a short discharge when there was for example an huge load while using the inverter it's even more weird: Then first the lower battery has an higher voltage than the upper with up to 14,5V (lower) / 13,9 (upper). While charging this is reversed so again the upper gets much higher voltage (up to 15,1V), just as described above.
Has anyone an idea what happens?