Hope someone can shed some light on this!
Our house bank is 345 amp @ 24v AGM batteries
(Sonnenschein). 8 years old, never discharged more than 30% to 70% SOC, about 100amps usage between charges. We've been charging batteries
by running generator
about 3 hours per day, first thing in the morning. The small solar
array we have left (in the process of upgrading solar) just barely manages to supply our load during the sunlight hours.
The typical charge rates we've seen on startup bulk charge is about 55-60 amps in bulk load (via our Victron 70amp Multi). The charge rate then drops as the batteries take a charge into the teens in adsorption mode and so on. After 3 or so hours we are in the high 90s% SOC. Every 3 or 4 days we make water
with our generator
after loading our batteries, which provides us enough extra power (max 20 amps available to charge batteries while making water) to top the batteries to 100%. We have been living like this all summer with no problem.
Then all of a sudden, three days ago, I noticed the bulk charge rate had dropped exactly in half (25 - 30 amps).
The same 1/2 charge maximum seems to happen under engine alternator
- was 80 - 90 amps on start-up bulk stage, now 40 - 45 max on start-up bulk.
It seems (this is only the third day so still observing!) that the 1/2 reduction is only in early bulk stage. The charge rate curve seems to catch up over time - so it is not taking twice as long to charge - just not as fast at the beginning (hope that makes sense!).
Nothing else seems to have changed. The daily loads are exactly the same.