One of the running costs for the house is batteries for the thermometers. There are 16 thermometers around the house with data loggers collecting their temperature all the time. Each one has a battery in. They are lithium, not sure of the original serial number but I've been replacing them with CR2s, since they sell them at the local electrical shop. Two for a thousand yen.
The thermometers are not essential to the running of the house, but useful in seeing how heat is flowing around it.
The batteries seem to last around six months, but I had to change a lot of them recently and I wondered, why not rechargables? I should have thought of it much earlier, but they didn't sell them at the electrical shop so I hadn't pursued it.
I found two types on the net. One was selling with a charger, so I got that. Unfortunatlely the batteries didn't seem to work very well. The data loggers came on when I put them in, but were still flashing "low battery". Not wanting to give up straight away, I ordered a couple of the other type, Ultrafire, that did not come with a charger. These were a little over half the price of the CR2s from the elctrical shop.
The Ultrafire batteries are 800 mAh, while the other ones were only 250. Not necessarily bad batteries but just smaller capacity. The voltage of batteries drops steadily as they loose charge, so a high capacity 3 volt battery may start at about 3.6 while a low capacity one just around 3. The data loggers, like many other semi-sentient electronic devices, judge the battery life by measuring its voltage.
The Ultrafire CR2s are still working a couple of months later, and I just ordered another four, in anticipation of having to change some batteries when I did my monthly data download. In the event, none of the batteries ran out this time, so I still have four ready for next time, and over the next six months I'll need to get 10 more so I can replace all of them.
The site I bought them from on Rakuten only ever says they have one or two packs of two in stock, although this may be because people usually only want one or two for their camera and a spare, so I'll have to ask them to let me order 5 packs.
