Battery issue

Jan 22, 2008
55
Hunter 376 Point Roberts
In the summer, I forgot to check my 2-T105 house batteries. All the cells (6 on the two batteries) were exposed and dry. After refilling them with distilled water I tested them with a voltmeter and they seem to hold the charge. I re-changed them and immediately after the charge they were 13.3V. I took them off from the charger and left them on the boat at 40F temperature, with no load for two weeks. Testing them again with the voltmeter showed 12.66 V.
The batteries were purchased in 2013, this is the first time I left them dry.
Just trying to figure out if they would last another season or should I just dish out some $$ for new to new T105-s?
 
Sep 25, 2008
7,077
Alden 50 Sarasota, Florida
It's unlikely but possible they may retain some of their original capacity. The only way to find out is do a proper load test.
 
May 17, 2004
5,032
Beneteau Oceanis 37 Havre de Grace
Like Don said you'll need to test them with a known load to find out what know of capacity they still have left. The voltage when it first came off the charger is just a surface charge, and the 12.66 resting voltage isn't great, but also isn't enough to really tell anything.
 
May 24, 2004
7,129
CC 30 South Florida
Load testing batteries can be a PITA but a ruined outing can be much worse. If I had any pending trips I would replace ($$$) them but if I just was going to hang around home base and do a few day sails I may put them through their paces to see if they are retaining charge and adequate capacity. I would make sure they are fully charged and promptly recharged after every use. 13.3V can be the voltage found right after charging while 12.66V is the normal voltage of a fully charged battery at rest. Now the question is how much capacity is stored behind that voltage; is it 90%, 75%,50% or 20%. At 90% the battery would have a very adequate capacity while at 20% the battery would discharge quickly; anywhere in between its adequacy would depend on the specific needs of the boater.
 
Oct 24, 2010
2,405
Hunter 30 Everett, WA
Yank one out and take it to a battery shop for load testing. If it's bad, change them both. As an alternative, you could purchase your own load tester. Most of us wouldn't use it frequently enough to justify having their own.

Ken
 
Aug 28, 2006
564
Bavaria 35E seattle
you could also have a battery shop run it through a 24 or 48 hour conditioning cycle, if the load test merits it.
 
May 24, 2004
7,129
CC 30 South Florida
What usually happens with a battery of diminished capacity is that we will discharge it deeper than the original threshold of 50% and we may not initially notice any fault. Well lets say we originally had a battery with a capacity of 110Ah but since it sulfated some now we have a battery with a capacity of 80Ah; can we safely take it down to 40Ah? You tell me. The reality is that we can, probably precipitating its demise without loss of functionality that is if our daily consumption is adequately met. How much longer will they last is anyone's guess.
 
Feb 7, 2018
6
tayana 37 mk11 houston tx
I let my starting battery go dry once, filled it then left on a 150 mile sail, when we went to start the genset which it also feeds, nothing dead as a door nail. Luckily the house batteries still had juice an we got started. load your battery up over suitable period and check voltage, also if you have battery charge indicator note amps out vs battery charge level.
 
Jan 22, 2008
55
Hunter 376 Point Roberts
Thanks guys...I think I will dish out some $$$ for two new ones. They are 5 years old so in a year or two they have to be replaced anyway. Considering that my boat has vacuum flush toilet, 12V windlass, fridge and freezer, autopilot, macerator, etc ....just too much to risk to die on me on a long weekend on the hook.
 
  • Like
Likes: Gunni