Batteries and the move to lithium

I had been planning to wait for the price of lithium to come down as these things always do after the first flush of invention. Unfortunately, that doesn’t look likely as the demand for lithium (life-po4) for the motor industry means that availability and prices elsewhere remain high.

However, the technology is definitely the way to go with charge rates high, weight low and usable capacity high too. This is also not the technology that are an explosion or fire risk which seems to be a common concern.

Our hand was forced somewhat since we bought new victron gel batteries in 2019. Being liveaboards with an inverter, we felt fortunate that we didn’t have to constantly go outside to reset a trip if we inadvertently put the kettle on with an electric fire and went over the power limit. The inverter charger would kick in, top up the power required from the batteries and then recharge them when we needed less power. However, there was a price to this convenience. Within fifteen months, our batteries were dead! Firstly we checked that everything was wired correctly and fortunately we have an all victron boat fitted to their standards. We kept investigating and victron agreed to replace our batteries under warranty which was a relief. We all thought we had just been unlucky.

However, nine months later, the same thing happened. We were on passage and a few hours after dark the boat went dark as the batteries died. Fortunately we could run the generator to provide our power requirements. Clearly something must be wrong but we were still at a loss.

Victron again offered to replace our Gel batteries like-for-like but also suggested an alternative. They felt that there must be something going on and that we couldn’t be so unlucky as to have two dud battery sets. They suggested that we upgrade to their lithium batteries which required less capacity to provide more usable power and they felt that we would hopefully not break the lithium! To sweeten the pill, they deducted the cost of the replacement batteries they would have provided and gave us some other incentives in price and some free equipment. It was still an eye watering amount but victron’s charity with replacement batteries wouldn’t last for ever.

However, we still needed to understand what was causing the problem. My current theory is that whenever we used more than the 16 amps coming from the shore power, the inverter pulled from the batteries and then replaced it later, which is effectively a small cycle of the battery. All batteries have a limited number of cycles and every time we used the kettle or marina her hairdryer in the winter it was a cycle, so potentially a number per day. The Gels would have had a few thousand cycles life but these could be being burned up at 10 a day. So in addition to the change of battery type, we also upgraded our shore power cables to provide 32amp power when available to reduce the cycling. That may have worked on its own but traditional mariadz belt and braces we did both!

Unfortunately, moving to lithium isn’t exactly plug and play from lead acid batteries and there are a number of factors to consider. Possibly most importantly is the alternator on the engine. Lithium like to take a charge, all you can give generally. Older technology alternators would just keep trying to give and would burn our very quickly from overheating. The changes we were making were coincide with the change of engine and so I cancelled the standard alternator being supplied and sourced a Balmar alternator with heat sensors from Oliver Ballham at Seapower. This alternator keeps going until it gets too warm and then shuts down. This isn’t too much of a problem for us since we have a lot of solar which can continue to top up the batteries if necessary.

Another area that needs work is the battery monitoring. On our initial test of the lithium we went away for a weekend and by the beginning of the third day had no domestic power at all! That’s just like the old batteries….. what we found were that the configuration variables of our charging systems were not accurate and so they stopped charging the lithium at too low a voltage meaning they weren’t fully charged, but the systems thought they were. We have since adjusted the variables across solar and battery monitoring so hopefully we have these right but there does seem to be an element of tuning. It was disconcerting though since the intelligent lithium batteries have clever electronics, and Bluetooth built in, which means that as soon as they get to a low state, they completely switch off. When this happened we went to our trusty generator which also didn’t start, a battery isolator switch that we never switch off had been flicked over. Still our engine started as always and put enough charge in for us to get going again. We then located the battery isolator problem and were back in business.

We know the engine alternator and the generator pump a lot of power into the lithium very quickly but we have yet to really see if there is any difference in the so,arc performance. In the UK, on a good summers day we were getting 5kwh, or half our battery capacity, from our 720W of solar. This would very much depend on the batteries though since they stopped pulling in too much power as they got fully charged. This often meant that we would switch on the water heater which uses 30A so that we had hot water and continued to maximise the solar. It will be interesting to see if these figures are different with lithium. Although our consumption will be the same, I am hoping that the batteries will take more charge before saying they are full. I will update this blog as we find out more…

In conclusion, we went from 10kwh of gel battery capacity (8 x 110Ah @ 12v) to a little less lithium (2 x 200Ah @ 24v). However, only about 50% of the gel batteries is usable energy whereas the lithium can be discharged safely to 80% so probably 50% more usable capacity in our new setup. These batteries are also half the size and probably half the weight so a lot easier to find them a home. We have yet to use these in anger on a proper crossing but feel more confident we now have a sustainable solution for ourselves,

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