Another Techie Bit – Batteries!


Not really a blog item. It’s another techie bit. Maybe hoping for a reader to pass comment?

When we first bought the boat, we knew that the batteries were the original ones, which makes them getting on for ten years old next year.  I’m guessing that if the engine hours are anything to go by, then the batteries have not really had nearly ten years of being cycled and being Victron AGM’s, they’re quite happy sitting on the shelf, they don’t self-discharge very much. So, perhaps we have a few more years left?

It was the major worry when we first bought her but it’s odd how “worries” sink down below other worries which rise up – like the dripping stern gland. It’s now three and a half years since we’ve owned the boat and there are signs of unhappiness in the battery department. When recharging them via the engine (it has a 230V alternator and so supplies the Victron box with up to 3.5 kW of juice), it’s set at 90A and the Victron used to go through it’s four stage charging – bulk (lots of amps), absorption (constant high voltage ~ 15 V, low current) and then float. Passing through a “battery safe” mode to limit initial current. It used to stay on bulk for a while but now it shifts to absorption after only a short time. An indication of lack of depth of charge? We’re not too worried as it goes and it stops. It never gets below 50% (usually never below 65%), so it shouldn’t be a worry.  I had to turn off the 4-stage charging as it went to float too quickly with the solar panels on.  It now does an eight hour absorption then floats.

One small and probably wildly inaccurate test was to use the Smartguage device which gives me a readout of the capacity in %. It went from 75% up to 90% in one hour. So that’s 90 amps for an hour. Meaning 90Ah represents an increase in 15% charge . . . scaling that up . . . 100% should equate to about 600AH, which is the stated capacity. A bit rough n ready but maybe they’re OK for a while anyway.

The cost of a new set – like for like is around £1200 plus fitting although I found a nice outfit in Market Harborough who would fit them for free (well, recouping the scrap value of £30 a battery covers that!). They will be a pig to get out, weighing in at 65 kg each and in an awkward place . . . .

I plan to disconnect em all and test each one to see if just one is a bit off. That’s for another day!