The TGS model does not have built-in batteries but can be connected and charged with external batteries.

"The UPS is offered in various versions:
TG: includes internal batteries for regular backup times
TGB: includes internal batteries and a connection for external battery packs for extended autonomy times
TGS: does not include internal batteries, but has a powerful charger for very long autonomy times"

Do not fall for it like I did... they don't mention that it requires an external battery and that it is sold without a battery... when you ask them to buy the battery, they don't have it to send to you and you have to search in the market.