I got a (relatively inexpensive) SmartYard LED Solar Spotlight as a gift, and have been playing around with ideas to extend the battery life. It uses a 3"x5" solar panel, and comes with a 3.7V, 1400mAh 18500 Li-ion battery.
There's extra room within the housing, so I originally considered the prospect of adding a second 18500 battery in parallel. However, several other posts here suggest there are multiple concerns/complexities associated with charging them in parallel, and with potentially unbalanced cells.
So now I'm thinking I could buy a single cell housing for an 18650 and use a (protected) 18650 instead of the 18500. The voltage is the same between the two, so presumably I'd get added battery life, with the only cost being it will take longer to charge.
Are there other issues I should be concerned about with this approach?