What's Going On With These Batteries?

[Cheechako]

Brand spanking new pair of batteries I put in my powerboat were 12.46 V at rest. That is after days of charging on land with no draw and after resting over night. Both batteries were within .01 V of each other.

[GrowleyMonster]

Originally Posted by philiosophy

I have a somewhat related question on battery maintenance. I was once told monthly equalizing was hard on batteries. He said take them down twice a year and bring them all the way up. Can someone give me a clearer idea of how far down and how long a charge to bring them all the way up. I have rare access to marinas, Do have a Honda 2.0 Thanks in advance

Monthly equalizing hard on batteries? Yeah, for a start battery or "dual use" battery or a so called deep cycle not robustly made. If you often operate for days on end with less than about 85% SOC, a monthly equalization might even be a good idea, for good heavy true deep cycle batts. That was my original intention, now I end up equalizing about twice a year. My boat mostly is only used for day trips or overnighters and I top up with shore power, so I don't think frequent equalizing is needed in my case. Cruisers often operate within the bulk charge zone for long periods of time and more frequent equalizing will probably extend battery life and increase performance significantly.


Current expert opinion seems to be that an annual discharge to 0% SOC is not particularly harmful for heavy duty deep cycle batteries. That doesn't mean discharge to zero volts!!!!! I assume yours is a 12v system and so a 0% SOC battery should show around 10.5v, but check the manufacturers figures for that. But it does not benefit the battery to do this, except that this is the ideal time to do a proper capacity test, which is really the only reason to discharge to 0% IMHO. An annual capacity test will tell you a lot about your batteries. Testing them individually is the smart thing to do. I would do this a few days after equalizing, same length of time after equalizing in every case, for a good comparison.



Well maintained deep cycle FLA batteries will show increased capacity over brand new ones the first year or two. Then they will slowly start falling off. When they get to about 80% rated capacity it is time to think about where you are going to get replacements because they are near the end of their useful life.



The more data you can record about your batteries, the better. Resting voltage, SG, average and deepest discharge, number of complete and incomplete charge/discharge cycles, etc. Water usage. Temperature. Log everything. Four years in on my propulsion bank, I am regretting not being more anal about logging my battery data. And up til now I have not done a proper capacitance test but I will do so, shortly after I return home from this job. Generally I have counted kwhrs used during approximately 50% discharge cycles at the 20hr discharge rate, and compared that to energy remaining as indicated by SG and resting voltage readings. This will put you in the ballpark if you trust your monitor/meter, but is nowhere near as accurate as a proper capacity test involving full discharge to 0%.

[john61ct]

Yes 10.5V is the standard for 0% with lead.


When testing or commissioning only, a dozen times over many years's lifetime will do no harm if:

be ready to stop immediately when it hits 10.49V and

immediately start charging.