Wednesday, February 15, 2012

The great battery experiment - interim findings

Whilst my heading today might have put off non boating readers, I know I have the rest of you in my grip.  Oooh yes. For a boater it is good to be obsessed about batteries, because unless you are, they will probably fail and let you down when you need them most.  One of the few grumbles I have heard from people with shared boats is that some of the owners don’t know or care about battery maintenance and ruin it for the others.  I’m also quite sure that half the moored boats you see with engines or generators running practically permanently would need to do that if they had looked after their batteries properly.

This week I was sorting out some old boat paperwork and came across the receipt for our last lot of new batteries.  Judging by the date, I reckon our current set have now done a good 200 charge / discharge cycles which is the point at which normal wet cell batteries would be starting to show signs of age i.e running down more quickly.   When I bought this set I took a gamble and bought some sealed units (Numax CXV) that claimed to go to 500 cycles.  So this year should start to reveal if it worked.  These batteries cost 15% more than standard open cell types, but I thought that if they did really have double the life, that would be a bargain.

So far, they are doing absolutely fine, helped considerably I reckon by the solar panel which keeps them up while we are not there and helps us to get charge up to a proper 100% when we’re cruising.   We very rarely need to let them go below about 70% charged which is also good for them. However there could yet be a dark harbinger of doom sealed inside their impenetrable casings.  Sealed batteries are risky because if they overcharge and bubble off gas, you can’t replace fluid.  I have no way of knowing if ours are full or not.   If they have gassed a lot then they will probably die this year and the extra 15% I paid for them will not have been worth it.  The literature on these batteries is very skimpy and doesn’t really tell you how they work.  You would think that the batteries could in some way condense and reuse some of any vapour that boils off, but that might be my wishful thinking.

I try to avoid the batteries gassing by carefully watching the charge voltage when we are cruising.  Once we get to 14.4v (above which boiling happens), I deliberately turn the fridge to a lower temperature to take the surplus power away from the batteries.  This works a treat because when you stop in the evening you can reset the fridge to its normal setting and being extra cold already, it uses less power overnight.  of course I don’t always spot it when the voltage goes a bit higher so I might have let them gas a bit.

Will the CXVs get me my extra money back, or have I been conned?  2012 holds the answer.  If they’re still doing well this time next year, I’m quids in.

P.S. Can you get treatment for battery OCD?


Anonymous said...

I was looking up 'domestic battery life' recently to find out how long they usually last but that just leads to depressing pages on assault in the home!
When I bought my boat, the owner told me had the 2 domestic batteries 'a couple of years' and I've had the boat for 6 years now. They are always more or less fully charged due to the solar panels but I wonder how much longer I can expect of them? The starter battery has been in the same legnth of time but that isn't charged by the panels. Still works, fingers crossed!

Neil Corbett said...

Knowing how little electricity you use Carrie, I'm not surprised your batteries last. I bet they never have to work hard I wouldn't be surprised if your solar panel met all your needs most of the year. Am I right in thinking you don't use a fridge?

Therefore your batteries might last a very long time - well they already have!


Halfie said...

You hit the nail on the head re. shared ownership boats and batteries!