Originally Posted by Bill Balme
Bill T: How do I tell if I have a bad cell vs. the batteries not being fully charged?
I've given the range of SG's before and after the supposed equalizing - I'm guessing the cells are OK - right? In which case, the cells must not have been fully charged - OR, the equalization cycle of the Prosine Inverter
is not working. How do I check that?
I'm thinking that if I charge the batteries - overnight - then do the equalization the following morning, if it doesn't get to 15+V something's wrong with the charger
- rather than the batteries...
I only have a simple hydrometer - needle moves through an arc
- is it any good? If it shows 1300, does that mean the cell is good? Is reading the SG right after a pseudo equalization flawed?
Appreciate the help...
I've never had any luck with hydrometers, despite having tried several rather diligently during a 2-year battery test. And, it's a sure way to get battery acid on you, your clothes, the battery box
, boat, etc. And, in my experience, they're really not needed.
One way to test for a bad cell is to charge the batteries fully, then turn off all switches and disconnect a cable from each battery
in the bank. This effectively isolates each battery.
Then, with a good digital multimeter check the voltage of each individual battery. If there is a significant difference between/among the batteries, then that battery likely has a weak or bad cell. If there's just a slight difference, it likely means that the capacities are slightly different or that all batteries in the bank didn't receive a full charge -- this can happen if multiple batteries in a bank are not connected correctly.
However, the fact that you measured SG approximately the same in all cells tends to indicate that the problem may have been elsewhere, e.g., the batteries not having been fully charged when you began.
It takes quite a while to reach full SOC and, very important, it takes a sufficiently high voltage. Most chargers/regulators/controllers/etc. are very conservative.
Flooded batteries and AGMs need 14.6 to 14.8VDC or so applied over a long period to reach full charge. How do you know when you've approached a 100% SOC? Monitor
the amperage going into the battery. When it drops to a very low level...say 0.5 or 1.0 percent of the AH rating of the battery bank, then the bank is "fully charged".
In a recent test, a large new AGM battery on charge @ 14.4VDC for a 4-hour period with a very big charger (200% of the AH capacity of the battery)....was still accepting 0.9% of its AH rating. With a less powerful charging
source, the battery would be accepting more than 1% after 4 hours @ 14.4VDC.