We recently had a discussion in another thread about how accurate the battery post mounted temperature sensor might be. As usual, there were a lot of different theories put out
, but that is always a good thing.
When we did our 80% discharge/recharge test a couple of days ago, I tried to get some idea of if the battery sensor reading seemed plausible, over the range of conditions.
By watching how long the temp stayed at max, once the van wasn't moving or running, I think I got a fairly good feel for how much of the temperature rise was because of the ambient air around the sensor and cable getting warmer from the exhaust, differential, and other underbody heat sources. Our batteries sit right behind the rear axle, but are somewhat heat baffled. The exhaust is also on one side of them, but baffled and insulated.
Bottom line is that we saw a max of about 30*F temperature gain at the battery temp sensors. When we stopped, we quickly lost about 7-9 degrees of that gain, and then the drop was very slow after that. It took almost 48 hours inside the shop, once we got home, for the batteries to get to ambient. My guess from this is that the first quick loss is getting rid of the ambient heat issues, and then the high thermal mass batteries slowly lose heat after that and would be a decent indication of actual battery internal temperature. That would leave us with about 22* of temp gain from putting in 350ah very quickly. It does point out that we really could benefit from temperature compensation on the alternator, also.
Since this is a really easy test to do during a recharge, I think it would be very interesting to see how other battery locations and charge rates react, temperature wise. I know many of the AGM installations are not in high ventilation or really cool areas, so they may have less of the ambient heat, but also be slower to cool, or they may not.
If those that have the capability to run a similar test feel like it, we might learn something, and help others with future installs if we see something that works better than other ways.