Backup Battery or what? (Calculator)

[Regtic]

http://i.imgur.com/qsZ0PM4.jpg

I opened up the back of the calculator to see what kind of battery I might have to replace eventually, but I didn't expect to see a second battery slot. Is it a backup battery slot? If so, how do I tell what kind of battery fits in there? I checked the manual, nothing in it about it. It's a SHARP EL-W535X

 

[Yellowflash]

I looked at it's manual here:
http://www.sharpmea.com/cps/rde/xbcr/documents/documents/om/30_cal/elw531-g-h-ha-w535_om_gb.pdf
But did not see it mention a backup battery. Maybe it uses both battery slots? Does the calculator work without having one of them?

Also, I have read that it is solar powered?

 

[Regtic]

I looked at it's manual here:
http://www.sharpmea.com/cps/rde/xbcr/documents/documents/om/30_cal/elw531-g-h-ha-w535_om_gb.pdf
But did not see it mention a backup battery. Maybe it uses both battery slots? Does the calculator work without having one of them?

Also, I have read that it is solar powered?

Nah it's totally battery powered and it works. It came with only the small one in it and it begs the question why that slot would be in the design in the first place. Seems inefficient and unnecessary considering the battery lasts like 3000 hours and there is no mention of there being a back up battery slot anywhere

also, it might even be a different manual since it has an x on the end of the model #

 

[Yellowflash]

I couldn't find anything online either. Maybe just ignore it.

 

[Vanadium 50]

Sharp has several calculators that use the same case. They use different batteries. Some use the smaller one, and others the larger.