Battery temperatures

[charles_reed]

Ever since the AC Delco "Freedom" batteries came out in the late 70's I've fought (on boats at least) a losing battle with them.

One of the first Ca++hardened plate batteries, I found them reluctant to charge and equally reluctant to give up their charge. Add to that the curious charging regime on which ACDelco insisted (from memory, equalising @ 15.5v).
4 years ago a contact proudly supplied me with a 95AH Freedom battery, so far I've ignored its vagaries. Unfortunately the two battery boxes in the aft cabin only accept sealed battery sizes, otherwise I'd have an open lead acid as being much more long-lived, reliable and less expensive.
Yesterday I went into the aft cabin and checked battery temperatures, the Freedom battery was hot to the touch, it's next door neighbour just warm.
The layout is for two aft batteries (90-95 AH) feeding through a 1-2-both switch and a forward 120 ah open battery, in permanent use as a domestic. The two aft batteries take it in turn to be reserved for engine starting. Feeding into the live circuit is the input from a BZ500 MPPT controller fed by 3 pairs of PV panels, totalling a nominal 320 watts. Charging is via an Iskia 110 amp alternator (I've bypassed the Adverc) and a Sterling ProCharge 20, with individual feeds to each battery.
Today, after 18hrs with no charge and overnight, fridge use, batteries had fallen to 28C for all except the AC Delco which was 34C. System volts were 12.3 (not resting).
On turning on the charger it went into bulk mode (first time this year), for 61', it then went into equalising charge for 1:35hrs (it's set for 4hrs) and then onto float.
Maximum system volts reached 13.9 and on float 12.9-13.1.
Both MPPT controller and charger are temperature compensated @ #1 battery (the AC Delco).
At cessation of equalising battery # 1(ACDelco) was @ 54C, the #2 battery next door was @ 40C and the forward battery @ 33C. You must realise that in Crete ambient temperatures are 35-40C during the day.
When I checked the volts, after being rested for 2 hrs, disconnected, the #1 was 12.87 #2 12.94 and the #3 (in use) 12.54.
Any theories as to why #1 battery is overheating (there is a definite whiff of sulphuric acid fumes above the open battery-box, so overheating it is.)

PS I reckon to get 10 years out of the forward battery and 5-7 out of aft batteries - the latter start the engine and run the fridge compressor.

 

[charles_reed]

Having searched, I've found one paper on thermal runaway in sealed lead acid car batteries - apparently quite common when they get above 50C.
One of the points made was that heat dissipation was a critical factor, now a blue battery (my #1), in a tight enclosure is less likely to be able to get rid of its heat than a black battery with no confining walls (my #3). Another interesting point, though claims made for sealed batteries were that they were as good as their flooded counterparts, life in a car proved they had about half the life, providing open ones were regularly topped up.
Nice to have ones prejudices confirmed.
Black open batteries are better than blue sealed ones.

 

[pmagowan]

There was an article in a recent PBO about this, including making a battery temperature monitor. Don't know much else I am afraid.

 

[Plevier]

Charles, can you isolate the hot battery and watch its voltage for a day or two?
I'm thinking you may have a (relatively) high resistance short in one cell which is producing heat with the charging current.
I had this recently on an Exide gel battery (no, I don't like gel batts but it came with the boat) that got very hot during a long engine run while an identical one in parallel stayed cool.
It fooled me at first because the OC voltage looked fine for most of a day after isolating it but then slid quite rapidly to about 10.5V as the bad cell discharged itself. It then stayed at 10.5V for a month until I took it to the recyclery.