Technically yes, however the battery won't last as long. The BOLT is designed to be a warming coffee mug and not a reheating coffee mug. It's a battery operated coffee warmer, so the BOLT heated mug is still governed by the laws of thermodynamics and power supply. Cold liquids require a lot of energy to come to temperature. If the BOLT is operating on battery power, it will use a large amount of that power to heat the liquid so you will have to charge it more frequently. The BOLT battery will usually last through multiple cups of coffee over the week. If you're heating cold coffee it would last for a single cup or two.
If you have the BOLT plugged in on the Heat AND Charge mode, then it will reheat the coffee without any issue, but may take longer to charge.
If you're looking for the best cordless coffee mug warmer or the best rechargeable heated coffee mug, the BOLT smart coffee mug is for you.