Another battery question

[Yngmar]

No cliff edge. Batteries degrade slowly in normal use, very slowly if they're fully charged by solar every day and you're only discharging to half empty. Or they get murdered and die suddenly from abuse (overcharge from faulty regulators seems most common). Deep discharge degrades them much faster, but it sounds like you're not doing that and treating them well, so no worries about sudden death. You can even get some capacity back with a desulphator (a thingie that fires high voltage spikes into them to shatter the crystals that have formed on the plates). Recommend not doing that with the boat electronics connected though, so probably something to play with in winter if you're thinking about extending their life another few seasons.

 

[pessimist]

No cliff edge. Batteries degrade slowly in normal use, very slowly if they're fully charged by solar every day and you're only discharging to half empty. Or they get murdered and die suddenly from abuse (overcharge from faulty regulators seems most common). Deep discharge degrades them much faster, but it sounds like you're not doing that and treating them well, so no worries about sudden death. You can even get some capacity back with a desulphator (a thingie that fires high voltage spikes into them to shatter the crystals that have formed on the plates). Recommend not doing that with the boat electronics connected though, so probably something to play with in winter if you're thinking about extending their life another few seasons.

Thank you. That's both what I wanted to hear and very helpful. I'll investigate a d.esulphator - I'd always assumed they were snake oil. Are they ok to use on sealed batteries.

 

[Yngmar]

Yes, I've had good success using one on our now spectacularly old AGMs from 2006 (still doing okay, not a full capacity anymore of course). The desulphators are rated for the capacity of a single battery, so you need to find one that suits yours usually biggish boat batteries and disconnect them from the bank and desulphate one by one or it won't work. It's been a few years since I did this so a bit fuzzy on the details, but I think it was at least 48h per battery. I did the lightbulb discharge test Paul describes before and after and they gained a good bit of capacity - can't remember how much, but it was significant. Sorry for being fuzzy on the numbers, it was in 2015 during a huge refit, and we've been cruising with these same batteries ever since.

Also, "sealed" just means they have little rubber cap "burp" valves under a glued on plastic lid. In fully charged and settled state you can pop that open and take a peek in there, which can quickly tell you a lot about the state of the insides. Close them back up before connecting anything though.

 

[pessimist]

Excellent - thank you again. Another job to add to the winter list.