Yes, sounds like battery problem.
First, let's identify which battery bank you are talking about.
Please verify that the shades operate on the HOUSE battery bank, not CHASSIS battery bank.
If house, that bank should charge from either engine (alternator) or from shore power/generator via your charger or inverter/charger.
If chassis, it should charge from engine and MAY, repeat MAY also charge from your charger or inverter/charger (not all are wired to charge from shore power/generator
OK from either alternator or charger or inverter charger, voltage at the batteries should be 13- 14.5 VDC.
As soon as charging source is removed, the batteries quickly dissipate their "surface charge" and drop to voltage of a 100% charged 12 VDC battery-- 12.7 VDC.
From there the voltage should drop very slowly (depending on amp draw and size of battery bank (in amp-hrs). 50% discharged is 12.2 VDC.
As an example, if your batteries are in good condition and fully charged and you have 4 6VDC golf cart batteries for your house bank (and the shades run on the house battery as I suspect they do) you have 440 amp-hrs @ 12 VDC. So, if you run a 10 amp load, it would take 22 hours to discharge your battery bank to 50%.
If the voltage drop is as quick (below 12.7 VDC) you very likely have one or more bad batteries. And if over a year or so old, replace all batteries that make up that bank.