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I just looked up when I bought my 5ah battery. I pulled it out of the storage box and it was reading zero volts.  It seems to be around April 2016. Given that such batteries really don't last that long, I'm not surprised it's dead.

The other battery I've tried to charge and it did reach 13v earlier in the day but after dark and when there was no solar power coming in, it dropped to 12.4v. That battery I seem to have bought in around July of 2017. Again, no great surprise that it's almost dead.

At 0v for the one and 12.4v for the other. I can say the small one is definitely dead. The larger one suprisingly still has 80% capacity but 80% capacity of a 7ah battery really isn't worth very much. That would be 5.6AH or around the capacity of two sets of 18650 batteres.

I had the solar water heater running today. The pump was certainly pushing the water through at a good rate. It didn't heat the water but there are probably 4 reasons for this:

1. The sun was not out for long and it was a bitterly cold day anyway.
2. I had a lot of tubing just laid out on the ground where heat would be lost.
3. The lid of the cooler in which I kept the water reservoir was not tight enough around the tubes so heat was probably lost that way too.
4. The heat exchanger design is not very efficient.

I'm thinking that the biggest issue is probably the air gap around the tubing. I have two small coolers. I'm not really sure I want to sacrifice one to just an experiment - even though they were dirt cheap. This is an experiment I want to return to but I want to go at it full tilt. I want to put black painted copper tubing and a lot of it - as the heat collector inside probably a Rubbermaid low-profile tub that's lined with some kind of insulator on the sides and bottom.  The tubing needs to be lagged between the heat exchanger and the water reservoir and the water reservoir needs to be fully closed so no heat can be lost from the reservoir. Having got that working, I then want to see what the difference between using the heat exchanger and using a straight sheet of glass over an insulated bucket of water. 

Meanwhile, today I had hoped to go under the bus to work on brake lines but the high point was 41F so a bit too cold to lie on cold ground. Tomorrow will be 71 but as I have to work on Monday and usually get a day's worth of tummy bugs from going under the bus, it'll have to wait til my 4 day weekend. Pretty much the same for working on the brake calipers.