Whilst you're giving out advice on batteries, here's another question:

[BobnLesley]

We have a set of four Trojan T-105s, about two years old, wired in series/parallel to provide a 450 amp/hr 12v bank and charged primarily from the solar panels plus the odd few hours (too many!) when we're motoring; I don't recall them ever having been plugged in to the mains battery charge, but in general they're working very well thanks.
However, whenever I've checked the electrolight levels - perhaps once every 4 - 6 weeks - if they've needed any top-up, it's invariably been one in particular that's needed any/the most; I'd just but this down to it being perhaps a less than perfect battery, until today: About six weeks ago I removed all the batteries to do another job in that locker and when I reinstalled them, I mistakenly re-located them in a different order within the locker; when I checked electrolight levels just now - the earlier post having reminded me that the job was overdue - I discovered that whilst only the one battery needed a top-up, it was a different battery to the usual one, it was however, the battery now located in the original 'problem' battery's position?

So rather than it being a specific battery that's water-hungry, I realise it's the battery in the furthest corner/last in line to the earth side of the circuit that requires topping up the most; my initial guess is that its location is probably the worst ventilated spot in the box, so it runs fractionally hotter and therefore suffers more evaporation? But I'd be interested to hear confirmation or otherwise of that theory.

 

[pvb]

Could be temperature related. Can you measure the battery temperatures when they've been charging on the engine?

 

[Deleted member 36384]

Mine are in my engine compartment, in series, +ve at the stern side, -ve at the bow side, about 1' away from the engine, if you image the engine compartment as a box, my batteries are in the port, aft corner. My positive battery (the aft most) is the one that needs topped up more than the others. Key point - with the boat sitting on the hard for nearly 2 years, with no engine running, this battery was still the one that required to be topped up with mains powered charging.

 

[Talulah]

It could be the way they are connected up.
Are the positive and negative supplies coming off the same battery or is the positive connected to the first battery with the negative connected to the last battery?
To even the load across batteries connected in parallel you need to do the latter.

 

[pvb]

It could be the way they are connected up.
Are the positive and negative supplies coming off the same battery or is the positive connected to the first battery with the negative connected to the last battery?
To even the load across batteries connected in parallel you need to do the latter.

Unless there are poor connections, that shouldn't make much difference with 4 batteries in series/parallel.

 

[tolhurstorganic]

Many multiple battery banks are connected together incorrectly with large imbalances of power being taken out/delivered back to different batteries. Its quite a subject and I am no expert. However when wiring up Naida I came across a very interesting website www.smartgaugeelectonics.co.uk go to Technical page 2 and find "How to correctly interconnect multiple batteries to form one larger bank" Good examples of incorrect practices and how to get it right.

 

[pvb]

Many multiple battery banks are connected together incorrectly with large imbalances of power being taken out/delivered back to different batteries. Its quite a subject and I am no expert. However when wiring up Naida I came across a very interesting website www.smartgaugeelectonics.co.uk go to Technical page 2 and find "How to correctly interconnect multiple batteries to form one larger bank" Good examples of incorrect practices and how to get it right.

Yes, but the OP only has 4x6v batteries, in a series/parallel configuration. There's little opportunity for imbalance unless the connections are very bad.

 

[William_H]

The way the battery banks are connected is unlikely to cause the observed problem. I would suggest that that place for that battery is warmer than the others or less ventilation. If it was a matter of connection so different current compared to the other parallel bank then one would expect the other series 6v battery to be the same. Curious but I would not worry. good luck olewill

 

[RobbieW]

Yes, but the OP only has 4x6v batteries, in a series/parallel configuration. There's little opportunity for imbalance unless the connections are very bad.

The link from the poster you quoted should have been http://www.smartgauge.co.uk/batt_con.html. I wouldnt dismiss the theory out of hand given the discrepancies described in that article, granted there wont be huge variance but it could be 33/66 and that could well stress one pair more than the other. That one position in a pair is getting through more water may be temp related though

 

[pvb]

The link from the poster you quoted should have been http://www.smartgauge.co.uk/batt_con.html. I wouldnt dismiss the theory out of hand given the discrepancies described in that article, granted there wont be huge variance but it could be 33/66 and that could well stress one pair more than the other. That one position in a pair is getting through more water may be temp related though

Although I subscribe to the principle of taking main feeds from opposite ends of a large parallel-connected bank (and indeed that's how I wired 6x110Ah batteries in my last boat), I'm doubtful of the accuracy of the figures in the Smartgauge article you've linked to. Unless there's something incredibly wrong with the connections, the OP's simple series/parallel bank would never have an imbalance anywhere near 33/66.

 

[RobbieW]

Although I subscribe to the principle of taking main feeds from opposite ends of a large parallel-connected bank (and indeed that's how I wired 6x110Ah batteries in my last boat), I'm doubtful of the accuracy of the figures in the Smartgauge article you've linked to. Unless there's something incredibly wrong with the connections, the OP's simple series/parallel bank would never have an imbalance anywhere near 33/66.

Heres the thing; whilst I have some idea of the background and experience of the articles author (Brian 'Gibbo' Gibson, one time Xantrex UK tech rep, creator of the SmartGuage/Smartbank devices & long term canal boat enthusiast) I have no knowledge of yours. So I'm inclined to take the figures on trust and, whilst mine were admittedly guessed, would expect that even in the simple case of 2 batts //ed together there would be some imbalance if the loads tail from the same pair. So if the OP finds they are tailed that way, and can easily change the wiring, theres a case for doing so.

The OP has also previously said hes in hot places, Florida in the last month or so. If any of the charging systems he has have batt temperature sensors, and those sensors have outputs that can be 'human read', theres a bit of diagnostic that could be done to test the idea of a hotspot by moving the sensor around to see if there is a difference whilst charging.

 

[pvb]

Heres the thing; whilst I have some idea of the background and experience of the articles author (Brian 'Gibbo' Gibson, one time Xantrex UK tech rep, creator of the SmartGuage/Smartbank devices & long term canal boat enthusiast) I have no knowledge of yours. So I'm inclined to take the figures on trust and, whilst mine were admittedly guessed, would expect that even in the simple case of 2 batts //ed together there would be some imbalance if the loads tail from the same pair. So if the OP finds they are tailed that way, and can easily change the wiring, theres a case for doing so.

I'm only a simple engineer, but it's obvious to me that there'd need to be something very wrong with the connections of only 4 batteries in series/parallel to cause an imbalance, certainly of the magnitude you suggested. And, if there was an imbalance, how come only one of the batteries showed overheating? Surely at least two would have?

The OP has also previously said hes in hot places, Florida in the last month or so. If any of the charging systems he has have batt temperature sensors, and those sensors have outputs that can be 'human read', theres a bit of diagnostic that could be done to test the idea of a hotspot by moving the sensor around to see if there is a difference whilst charging.

See post #2.