CuddeView 4-in-1 Field Viwer Owner's Manual page 11

Or you could charge the battery by AC adaptor (not
supplied) to a power outlet. Any USB AC adapter will
function with CuddeView.
Battery power status
CAUTION
* It takes approximately 4 hours to fully charge a depleted battery.
* The photo viewer can be charge at ambient temperatures between 0℃
(32℉) and +40℃ (104℉).
* The battery does not need to be fully discharge or exhausted before
being recharged.
* Lithium-ion battery loses their charge even when not used. So, be sure
to charge the battery before use.
* To ensure that your battery lasts as long as possible, switch the photo
viewer off when you are not using it.
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