I purchased myself some 18650 batteries from China – 8 in total. For those who are unfamiliar with 1860 batteries, they are 18mm in diameter and 65mm long. They are Lithium Ion batteries with a voltage of 3.7 volts.
These batteries fit in a battery box that fits VERY snugly in the main Electronics box. Alas…on the first test, the batteries failed after 30min of operation. It turned out that one of the batteries died – collapsed. This apparently happens if too much current is drained from these batteries, or they are charged with a charger in a ‘bad’ (over voltage?) way. That is apparently why most 18650 incorporate a circuit protector to stop this from happening. (When they have this circuit protector added…they are typically a few more mm longer).
I suspect I’ll need to invest in more expensive (non-China 18650 batteries).